THE  CHEMISTRY  AND  PHYSICS 

OF 

DYEING 


THE  CHEMISTRY  AND  PHYSICS 

OF 

DYEING 


BEING  AN  ACCOUNT  OF  THE; 

RELATIONS  BETWEEN  FIBRES  AND  DYES, 

THE   FORMATION    OF    LAKES,  AND    THE 

GENERAL  REACTIONS  OF  COLLOIDS,  AND 

THEIR  SOLUTION  STATE 

BY 

W.  P.  DREAPER,  F.I.C.,  F.C.S. 

ILLUSTRATED  BY  CURVES  AND  NUMEROUS 
TABULATED  RESULTS 


LONDON 
J.     &     A.     CHURCHILL 

7  GREAT  MARLBOROUGH  STREET 
1906 


, 


<K 


PREFACE 

IN  the  present  volume  an  attempt  is  made  to  collect 
and  classify  the  work  which  has  been  brought  for- 
ward to  explain  the  action  of  dyeing,  mordanting 
and  lake  formation. 

The  general  text-books  on  dyeing  devote  little 
space  to  this  particular  side  of  the  question.  They 
deal  with  the  operations  of  the  dye-house,  rather 
than  with  the  principles  which  seem  to  govern  the 
actual  practice  of  this  branch  of  industry. 

It  is  advisable  that  the  modern  dyer  should  have 
some  knowledge  of  the  general  reactions,  which  give 
rise  to  the  results  obtained  in  the  many  processes, 
involved  in  the  dyeing,  and  bleaching  of  textile  fibres. 
Without  some  such  knowledge,  it  is  difficult  to 
appreciate  their  nature ;  or  be  in  a  position  to  control 
their  working  in  a  systematic  manner. 

To  obtain  this  under  present  conditions,  it  is 
necessary  to  make  a  more,  or  less,  tedious  search 
over  the  scientific  and  technical  journals  of  the  last 
thirty  years. 

This  same  difficulty  presents  itself  to  the  student, 
who  wishes  to  engage  in  research  on  this  interesting, 
but  little  understood  subject. 

It  is,  perhaps,  equally  difficult  for  the  dyer  to 
obtain  information  of  those  branches  of  physical 
science,  which  will  possibly  give  an  explanation 
of  many  of  the  mordanting  and  dyeing  operations 
met  with  in  daily  practice. 

With  the  extension  of  our  knowledge  of  general 
physics,  and  the  breaking  down  of  the  artificial 


vi  PREFACE 

barriers  set  up  during  the  nineteenth  century  be- 
tween the  different  branches  of  experimental  science, 
has  come  a  wider  outlook.  The  subject  before  us 
forms  an  interesting  chapter  in  the  evolution  of 
theoretical  speculation  in  its  application  to  the 
principles  of  a  well-known,  but  little  understood 
industrial  process. 

From  the  very  nature  and  complexity  of  the 
subject,  it  is  more  than  likely,  that  any  further 
advance  in  our  knowledge  will  come  from  within 
the  industry  itself.  With  the  increasing  number 
of  chemists  who  are  devoting  their  time  to  this 
subject,  and  gradually  displacing  the  "  rule  of 
thumb  "  methods  of  the  past,  this  does  not  appear 
to  be  improbable. 

At  the  present  time,  the  art  of  dyeing  may  be 
said  to  be  in  advance  of  the  science  of  the  subject. 
The  first  step  towards  restoring  the  balance,  is 
to  take  a  general  survey  of  the  work  done  in 
the  past,  by  the  many  investigators  who  have  given 
this  matter  their  attention.  The  foundation  on 
which  we  rest  our  present  ideas  of  the  nature  of 
the  dyeing  phenomena  met  with  in  our  dye-houses, 
and  finishing  factories,  must  be  realised  before  any 
further  advance  is  possible.  The  subject  has  been 
treated  from  this  point  of  view.  The  object  of  this 
book  is  to  give  the  practical  dyer,  and  student,  a 
collected  record  of  the  work  done  in  the  past,  so 
that  it  may  be  available  for  reference. 

It  is  only  by  referring  back  the  observed  pheno- 
mena in  dyeing  to  the  first  principles  of  chemistry 
and  physics,  that  we  can  expect  to  advance  beyond 
the  present /state  of  uncertainty  as  to  the  nature  of 
the  actions  involved. 

The  need  for  further  research  along  systematic 
lines  is  urgent.  Much  might  be  done  in  the  dye- 
ing departments  of  our  technical  institutions,  if  a 
definite  scheme  of  research  could  be  devised,  and 
carried  out. 


PREFACE 


vn 


Then,  perhaps,  the  process  of  dyeing  with  all 
that  it  entails,  will  take  its  place  in  the  general  scheme 
of  physical  science. 

A  study  of  the  name  index  indicates  how 
little  of  this  work  has  been  done  in  England,  and 
the  steps  which  are  necessary  in  the  future,  if  this 
country  is  to  hold  its  own  in  the  dyeing  industry. 

The  dyer  must  watch  other  things  besides  his 
dye-pots,  and  his  tinted  yarns.  He  must  know  some- 
thing of  the  general  reactions  of  colloids,  as  typical 
of  those  which  may  possibly  take  place  in  the  sub- 
stance of  the  materials  he  has  to  prepare,  and  dye. 
It  is  important  too,  that  he  should  have  some  know- 
ledge of  the  general  principles  which  seem  to  govern 
solution,  and  the  action  of  temperature,  &c.,  on  the 
dye  liquors,  and  fibres. 

This  book  is  therefore  written  to  supply  the 
practical  man  with  this  knowledge.  It  is  also  hoped 
that  it  may  induce  the  student  to  embark  on  original 
work,  and  by  supplying  him  with  an  outline  of  what 
has  been  already  done  on  the  subject,  indicate  new 
lines  on  which  further  work  may  be  undertaken 
with  advantage.  A  close  study  of  this  subject  on 
systematic  lines,  and  in  its  wider  aspect,  cannot  fail 
to  lead  to  important  results. 

It  is  difficult,  under  present  conditions,  to  entirely 
do  away  with  the  divisions,  which  still  exist  in  con- 
nection with  the  study  of  dyeing  phenomena.  While 
sympathising  with  those  who  are  ready  to  take 
this  step,  the  author  feels  that  had  this  book  been 
written  on  these  lines,  it  would  have  been  less  useful 
to  the  majority  of  readers. 

It  is  quite  possible  for  the  student  to  steer  a 
middle  course,  and,  keeping  for  convenience  the  old 
divisions  before  him,  to  remember  that  the  general 
scheme  of  research  is  an  artificial  one  at  best,  and 
that  the  recognised  divisions  are  of  an  arbitrary 
nature.  This  is  being  demonstrated  daily.  All  that 
the  student  in  dyeing,  or  the  practical  dyer,  needs  to 


viii  PREFACE 

remember  is,  that  these  divisions  are  upheld  on  the 
grounds  of  general  convenience. 

To  the  general  student  of  chemistry  it  is  doubtful 
whether  there  is  at  the  present  time  a  more  fruitful 
subject  of  research  than  that  of  dyeing.  It  is  hoped 
that  the  publication  of  the  chief  work  which  has  been 
done  on  the  subject  in  the  past  in  the  present  form 
will  tend  to  increase  the  interest  taken  in  this 
subject,  and  at  the  same  time  raise  the  standard  of 
the  work  done. 

Wherever  possible,  references  have  been  given 
to  the  original  communications  in  which  the  recorded 
facts  have  first  appeared,  in  order  that  fuller  knowledge 
may  be  obtained  for  special  purposes. 

The  facts  mentioned  under  their  different  head- 
ings are  also,  as  far  as  possible,  put  forward  in  their 
historical  sequence. 

In  this  way  the  gradual  development  of  the 
subject  under  review  may  be  followed  from  the 
earliest  investigations,  and  speculations,  of  Hellot 
in  the  year  1734  to  the  present  time  ;  and  an  insight 
into  the  probable  nature  of  dyeing  obtained. 

This  can  hardly  fail  to  be  of  interest  to  the  dyer, 
whose  aim  should  be,  first  of  all,  to  understand  the 
principles  which  control  the  many  and  varied  opera- 
tions of  dyeing,  and  by  this  means  obtain  [more 
regular  and  satisfactory  results  in  the  practice  of  his 
art. 

The  author  wishes  to  express  his  thanks  to  Mr. 
W.  A.  Davis,  B.Sc.,  for  his  help  in  the  revision  of 
proofs  and  for  his  valuable  suggestions. 

THE  AUTHOR. 

v 

September  15,  1906. 


CONTENTS 

CHAP.  PAGE 

I.  HISTORICAL  INTRODUCTION     .         ,         .         .  .  i 

II.  PROPERTIES  OF  FIBRES,  AND  THEIR  REACTIONS  .  n 

III.  DYES  AND  LAKES,  AND  THEIR  PROPERTIES     .  .  32 

IV.  ACTION,  AND  NATURE  OF  MORDANTS     .         .  .  53 
V.  STATE  OF  FIBRES,  AND  ACTION  OF  ASSISTANTS  .  72 

VI.  SOLUTION,  AND  THE  PROPERTIES  OF  COLLOIDS  .  102 

VII.  PHYSICAL  ACTION,  AND  SOLID  SOLUTION        .  .  140 

VIII.  EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING.  .  181 

IX.  EVIDENCE  OF  CHEMICAL  ACTION    IN    DYEING 

(continued)         .          .          .          .          .          .  .208 

X.  PART  PLAYED  BY  COLLOIDS  IN  DYEING,  AND  LAKE 

FORMATION       .         .         .         .         .         .  .  234 

XL  THE  ACTION  OF  LIGHT  ON  DYEING  OPERATIONS,  AND 

DYED  FABRICS          .         .         .         ;         .  .  281 

XII.  METHODS  OF  RESEARCH        .         »         .         .  .  297 


LIST   OF  ILLUSTRATIONS 

CURVES 

FIG.  PAGE 

1 .  Formation  of  Lakes  in  Aqueous  Solution                  .  .          44 

2.  Absorption  of  Sulphuric  Acid  by  Wool            .         .  .          88 

3.  Influence  of  Time  on  Absorption  of  Acid      .          .  .          89 

4.  Rosaniline  Acetate  on  Wool          .         .  99 

5.  Absorption  of  Tannic  and  Gallic  Acids  in  presence  of 

Acetic  Acid       .         .          .         ..          .  .        162 

6.  Absorption  of  Gallic  Acids  by  Colloids  .  .        164 

7.  Fastness  of  Ingrain  Colours  (phenolic)  .         .          .  .        202 

8.  Fastness  of  Ingrain  Colours  (amine)      .         .         .  203 


CHEMISTRY  AND  PHYSICS 
OF  DYEING 

CHAPTER   I 
HISTORICAL  INTRODUCTION 

THE  art  of  dyeing  has  been  practised  for  long  ages. 
Its  origin  is  lost  in  antiquity.  There  is  distinct 
evidence  that  operations  of  this  nature  were  carried 
on  in  Persia,  Egypt,  the  East  Indies,  and  Syria  in 
early  days.  The  Tyrians  excelled  in  the  produc- 
tion of  the  celebrated  purple  of  Tyre,  and  seem  to 
have  made  its  manufacture  one  of  their  chief  occu- 
pations. This  colour  was  noted  for  its  richness, 
and  durable  qualities.  It  is  believed  that  the 
method  of  dyeing  this  colour  was  invented  about  the 
year  1500  B.C.  Wool  dyed  in  this  way  sold  in  Rome 
at  a  price  equivalent  to  £30  per  pound. 

The  purple  of  Tyre  seemed  to  vary  in  its  colour. 
Pliny  mentioned  that  the  shade  varied  from  a  faint 
scarlet  to  the  red  of  coagulated  bullock's  blood. 

The  origin  of  the  shell  fish  from  which  the  colour 
was  developed  seemed  to  determine  the  shade. 
The  Atlantic  variety  gave  the  darkest  colours, 
while  those  obtained  off  the  Phoenician  shore  yielded 


2V      ::  CHEMISTRY  AND   PHYSICS   OF   DYEING 

:  ^  ^tfie' scarlet  ^shades.  The  dye  prepared  from  these 
varieties  of  shell  fish  was  probably  developed  by 
some  process  of  oxidation  ;  the  exact  nature  of  the 
operation  being  unknown. 

The  secret  of  the  production  of  this  colour  was 
carefully  guarded,  and  in  this  way  a  virtual  mono- 
poly was  established. 

i  It  was  not  until  the  fourteenth  century  that  the 
art  of  dyeing  flourished  in  Europe.  Florence  was 
one  of  the  headquarters  of  this  industry. 

An  inferior  cochineal,  or  kermes,  was  collected 
by  the  Arabs  about  this  period. 

This  same  product  was  known  to  the  Greeks  and 
Romans  under  the  name  coccus.  It  is  interesting 
to  note  that  between  the  ninth  and  fourteenth 
centuries,  the  rural  serfs  were  obliged  to  deliver  to 
the  convents  a  certain  quantity  of  this  dye  annually, 
i  A  great  deal  of  this  German  kermes  was  consumed 

in  Venice  for  the  dyeing  of  scarlet. 

Pliny  ("Hist.  Nat."  lib.  xxxv.  cap.  n)  draws 
attention  also  to  the  extraordinary  method  of  dye- 
ing linen  in  Egypt.  They  clearly  developed  the 
colour  on  mordants  in  this  case. 

A  great  change  came  about  in  the  dyeing  in- 
dustry with  the  discovery  of  America.  With  the 
trading  which  sprung  up  between  the  two  continents 
many  very  valuable  dyewoods  were  introduced  to 
Europe.  Among  these  may  be  mentioned  cochineal, 
logwood  and  annotto. 

/  About  this  time  also  Oricelli  discovered  the  action 

of  ammoniacal  liquors  on  certain  lichens  with  the 


HISTORICAL   INTRODUCTION  3 

production  of  coloured  bodies  which  might  be 
used  for  dyeing  organic  fibres.  These  have  only 
given  way  before  the  aniline  colours.  A  great 
development  took  place  about  the  year  1650,  when 
tin  salts  were  introduced  as  a  mordant  in  the  place 
of  alum  ;  and  with  this  introduction  we  have  the 
production  of  the  first  really  brilliant  colours  on 
fibres.  As  the  result  of  the  discovery,  a  large  dye- 
house  was  established  at  Bow.  Cochineal  was  dyed 
on  this  mordant  with  great  success,  and  the  colours 
produced  in  this  district  were  justly  celebrated 
for  their  purity  and  beauty. 

In  the  year  1548  the  first  text-book  on  dyeing 
appeared.  The  production  and  publication  of  this 
book  had  a  great  effect  on  the  art  in  Germany, 
France  and  England.  The  dyeing  operations  in 
these  countries  were  greatly  extended  as  a  result ; 
and  the  almost  complete  monopoly  which  had 
existed  for  nearly  a  century  or  more  in  Italy  was 
gradually  broken  down  by  this  natural  extension 
of  the  industry.  The  year  1667  was  a  most  im- 
portant one  for  England.  A  Fleming  coming  to 
England  brought  with  him  the  art  of  dyeing  wool 
in  a  state  of  great  perfection.  Since  that  date  it 
has  been  maintained  at  a  high  level  in  this  country, 
and  sets  a  standard  to  the  world. 

With  this  increased  activity  came  the  publica- 
tion of  several  works  on  the  subject.  This  greatly 
widened  the  interest  taken  in  this  important  and 
lucrative  branch  of  industry. 

The   dyeing   with   woad  was   of   importance   in 


4  CHEMISTRY   AND   PHYSICS   OF   DYEING 

this  country,  and  the  introduction  of  indigo,  with 
its  superior  colours  on  wool,  created  a  scare  amongst 
those  interested  in  the  woad  industry.  Severe 
measures  were  taken  by  the  government  to  keep 
this  product  out  of  the  country.  It  was  not  until 
the  reign  of  Charles  II.  that  its  use  was  permitted 
in  the  English  dyehouse. 

As  might  be  expected  it  gradually  replaced  the 
native  woad,  until  to-day  the  latter  is  only  used 
in  limited  quantities  for  the  "  indigo- woad  "  bath 
in  some  special  dyeing  districts. 

In  the  eighteenth  century  the  art  made  great 
progress.  About  this  time  madder  was  used  in 
large  quantities  and  quercitron  introduced.  Mor- 
dants were  also  manufactured  in  a  purer  state,  with 
the  natural  result  that  the  colours  were  correspond- 
ingly brighter  in  shade  and  of  increased  beauty. 

Mineral  colours  were  also  introduced  and  used 
in  the  colouring  of  fibres,  being  precipitated  in  their 
substance.  In  the  year  1734,  Hellot  published  his 
celebrated  book  on  wool-dyeing,  and  this  again  led 
to  the  natural  extension  of  the  industry.  "  L'art 
de  la  teinture  des  laines  et  des  etoffes  de  laine"  was 
a  most  important  work,  and  its  influence  was  great 
on  the  industry. 

About  this  time,  also,  the  value  of  Turkey  red 
as  dyed  in  India  gradually  impressed  the  European 
dyers  with  its  great  and  almost  unique  value.  As  a 
result  of  this,  the  French  government  in  1765  caused 
the  details  of  this  process  of  dyeing  to  be  published. 
To-day  the  seat  of  this  industry  is  in  Europe, 


HISTORICAL   INTRODUCTION  5 

although  it  may  possibly  drift  back  to  the  East 
again.  Two  other  important  books  were  published 
in  France  during  this  century. 

Le  Pileur  d'Apligny  in  1776  published  "  L'art 
de  la  teinture  des  fils  et  etoffes  de  coton/' 
which  has  been  generally  recognised  as  marking  a 
stage  in  the  development  of  this  subject. 

"  Les  elements  de  Fart  de  la  teinture/'  by 
Berthollet,  published  in  1791,  and  "  La  chimie 
appliquee  aux  arts/'  by  Chaptal,  in  1807,  greatly 
added  to  the  knowledge  of  dyeing. 

These  publications  undoubtedly  tended  to  give 
to  France  that  superior  position  which  she  has  so 
long  held  in  the  art  of  dyeing.  Their  influence  is 
difficult  to  over-estimate.  The  list  of  important 
books  published  in  France  on  this  subject  must  also 
include  the  following: 

"  Legons  de  chimie  appliquees  a  la  teinture/' 
by  Chevreul  in  1828-1831  ;  "  Traite  de  chimie 
appliquee  aux  arts/'  in  1828-1846;  "  Legons  de 
chimie  industrielle/'  by  de  Girardin,  published  in 
J837  ;  "  Traite  theorique  et  pratique  de  1'impression 
des  tissus/'  by  Jean  Persoz  (1846)  ;  "  Cours  elemen- 
taire  de  teinture/'  de  Vitalis  (1823)  ;  "  Manuel 
complete  de  teinture/'  Vergnaud  (1832). 

Another  great  step  in  dyeing  as  practised  in 
Europe  was  taken  during  the  early  part  of  the  eight- 
eenth century.  Calico  printing  in  its  rudimentary 
stage  was  introduced.  This  industry  has  grown  to 
enormous  proportions.  This  very  rough  sketch  of 
the  early  days^of  dyeing  brings  us  up  to  the  time 


6  CHEMISTRY   AND   PHYSICS  OF   DYEING 

when  dyers  began  to  study  the  theoretical  basis  of 
their  operations,  and  to  trace  the  possible  actions 
of  dyes  and  fibres ;  and  the  part  which  they  respec- 
tively played  in  the  process  of  dyeing. 

From  these  early  speculations  by  easy  stages  our 
knowledge  of  this  subject  has  gradually  developed. 
When  we  look  back,  remembering  the  elementary 
state  of  scientific  knowledge  of  those  days,  and  the 
admittedly  complex  nature  of  the  processes  of 
dyeing,  we  cannot  but  give  a  full  measure  of  praise 
to  the  work  of  the  early  investigators,  before  whose 
eyes  the  first  opening  out  of  this  subject  must  have 
been  of  great  interest. 

Even  to-day,  with  our  extended  knowledge,  we 
are  yet  ignorant  of  the  exact  and  complete  causes 
which  bring  about  many  of  the  complicated  and 
varied  effects,  which  are  classified  under  the  com- 
prehensive term,  dyeing. 

Much  of  the  detail,  at  any  rate,  is  little  under- 
stood. From  the  simpler  speculations  of  these 
investigators,  and  their  rough  experiments  on  pound- 
samples  of  wool,  the  student  of  to-day  may  derive 
valuable  information  and  an  insight  into  the  early 
methods  of  dyeing. 

At  the  present  time  we  are  passing  through  a 
transition  state,  and  until  the  general  ideas  of 
molecular  physics  and  chemistry  reach  a  more  satis- 
factory and  sure  basis,  it  is  difficult  to  expect  that 
our  knowledge  of  the  operations  of  dyeing  can  rest 
on  a  sure  foundation. 

It  is,   however,   certain   that    if    the    study   of 


HISTORICAL   INTRODUCTION  7 

dyeing  betaken  up  in  the  proper  spirit,  the  results 
obtained  must  influence  on  their  side,  either  by 
confirmation  or  otherwise,  many  of  the  most  im- 
portant speculations  in  the  domain  of  solution,  and 
other  equally  important  phenomena.  The  abnormal 
nature  of  the  reactions  in  dyeing,  and  the  very 
delicate  nature  of  the  available  colour-tests,  com- 
bine to  present  us  with  an  effective  means  for 
further  investigations  into  the  state  of  matter,  under 
favourable  conditions.  This  point  is  not  so  generally 
recognised  as  it  should  be,  owing,  perhaps,  to  the 
intimate  knowledge  of  the  practical  part  of  the 
question,  which  is  necessary  before  the  facts  ob- 
served in  the  dyehouse  can  be  given  their  true  signi- 
ficance. This  is  only  obtainable  by  direct  contact 
and  continued  observation  of  the  dyehouse  routine. 
In  this  way,  and  this  way  only,  will  many  abnormal 
conditions,  and  results,  yield  to  the  investigator 
their  true  significance. 

In  the  earliest  days  there  were  the  up- 
holders of  mechanical  and  chemical  theories  of 
dyeing.  Ever  since  the  middle  of  the  eighteenth 
century,  the  conflict  has  raged  round  these  two 
hypotheses,  greatly  to  the  benefit  of  our  knowledge 
of  dyeing.  In  the  search  after  fresh  evidence 
many  new  and  important  facts  have  come  to  light. 
The  influence  of  this  has  been  satisfactory,  and  has 
led  to  improvements  in  the  processes  of  dyeing,  and 
the  gradual  recognition  of  the  fact  that  scientific 
methods  are  necessary  in  the  dyehouse.  To-day  we 
have  other  possible  explanations  of  the  causes  of 


8  CHEMISTRY   AND   PHYSICS   OF  DYEING 

dyeing,  which,  however,  in  their  broadest  terms,  may 
still  be  referred  back  to  these  early  and  rival  ones. 

There  is  a  tendency  at  the  present  time  to 
discard  such  artificial  barriers  as  divide  the  opera- 
tions of  nature  into  almost  watertight  compartments. 
The  terms  mechanical,  physical,  and  chemical,  are 
more  and  more  regarded  as  mere  phases,  referring 
phenomena  back  indirectly  to  a  common  origin  of 
matter  and  force. 

It  is  not  necessary  for  the  dyer  altogether  to 
discontinue  those  divisions  of  the  past,  which  by 
their  very  limitations  have  led  to  the  necessary 
concentration  of  ideas  along  certain  lines.  The 
time  is  not  yet  come  when  we  can  do  so  with  any 
certainty  or  advantage.  To  the  present  system 
we  must  at  least  ascribe  our  present  position.  It 
is  doubtful  if,  for  some  time  to  come,  any  advantage 
would  be  gained  by  giving  up  these  general  divisions, 
which  have  proved  so  useful  in  the  past.  At  the  same 
time,  the  student  must  keep  an  open  mind  on  this 
subject.  There  is  no  indication  that  the  problem 
before  us  of  indicating  the  true  cause  of  dyeing  is 
becoming  less  complex  in  its  nature.  Some  new 
principle  or  factor  in  general  physics  may  be  applied 
to  dyeing  operations,  and  in  this  way  our  knowledge 
may  be  greatly  extended.  To-day,  other  theories 
besides  those  already  mentioned  have  their  upholders. 
Dyeing  has  been,  for  instance,  associated  with  "  solid 
solution/'  and  an  attempt  has  been  made  to 
extend  this  state  to  cover  the  absorption  results 
when  a  dye  is  taken  up  by  an  organic  fibre.  From 


HISTORICAL  INTRODUCTION  9 

another  point  of  view  the  dyeing  effect  has  been 
ascribed  to  "  dissociation  effects." 

Our  increasing  knowledge  of  the  general  reactions 
of  colloids,  in  which  class  we  may  include  the  textile 
fibres,  is  modifying  our  views  ;  and  the  condition- 
reactions  of  these  complex  bodies  has  given  rise  to 
what  is  termed  the  "  colloid  "  theory  of  dyeing. 

The  time  has,  perhaps,  come  when  it  is  necessary 
to  classify  the  researches  of  the  past  in  this  and 
kindred  subjects,  and  formulate  the  general  conclu- 
sions which  have  been  arrived  at  from  time  to  time, 
and  examine  them  from  the  practical  dyers*  point  of 
view.  It  is  unfortunate  that  the  majority  of  in- 
vestigators have  contented  themselves  with  working 
on  a  qualitative  rather  than  a  quantitative  basis. 
Little  care  has  been  taken  to  work  with  pure  materials 
on  the  one  hand,  or  under  recorded  conditions  on 
the  other.  It  is,  therefore,  difficult  to  form  an 
estimate  of  the  reliability  of  the  recorded  results  in 
many  cases  where  accuracy  of  detail  and  conditions 
are  of  the  first  importance. 

No  doubt,  our  further  inquiries  into  this  subject 
will  enable  us  to  classify  more  correctly  the  recorded 
results  of  the  past  than  is  possible  at  the  present 
time. 

Space  has  been  devoted  to  the  consideration  of 
our  present  general  knowledge  of  the  properties 
and  nature  of  colloids,  and  a  short  resume  of  the 
work  done  on  this  subject  has  been  included  in  this 
work.  The  abnormal  actions  of  these  substances  in 
a  state  of  solution  are  of  great  interest  to  the  dyer. 


io  CHEMISTRY   AND    PHYSICS   OF  DYEING 

They  seem  to  approximate  to  the  results  obtained 
in  the  dyehouse. 

For  full  details  of  the  chemical  constitution  of 
the  dyes  used  to-day,  the  standard  text-books  on 
this  subject  must  be  consulted.  As  regards  the 
possible  actions  in  the  operations  of  dyeing  in  rela- 
tion to  their  constitution,  the  matter  is  dealt  with 
in  this  work  in  an  elementary  way. 


CHAPTER  II 
PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS 

So  much  has  been  written  on  the  properties  of  the 
fibres  themselves  in  their  physical  aspect,  that  no 
great  space  will  be  devoted  to  this  subject.  This 
matter  should,  however,  receive  careful  attention, 
and  the  standard  works  on  the  subject  should  be 
consulted. 

The  most  important  properties  of  the  leading 
fibres  are  briefly  reviewed  here. 

For  our  purpose  we  may  fairly  recognise  the 
accepted  classification  of  the  fibres  into  those  of 
animal  and  vegetable  origin  respectively. 

From  the  present  point  of  view,  our  knowledge  is 
mainly  confined  to  the  three  important  fibres,  silk, 
wool,  and  cotton.  So  far  as  the  others  are  concerned, 
with  perhaps  the  possible  exception  of  jute,  little  work 
has  been  published.  In  these  cases  dyeing  is  of  an 
empirical  nature,  whatever  may  be  said  of  our 
knowledge  in  the  first  mentioned  cases. 

It  is  strange  that  more  attention  has  not  been 
given  to  the  reactions  entailed  in  the  dyeing  and 
mordanting  of  these  other  fibres.  A  systematic 
and  regular  survey  of  the  comparative  reactions  of 


12  CHEMISTRY  AND  PHYSICS  OF  DYEING 

these  towards  dyes,  &c.,  in  relation  to  their  physical 
nature,  could  not  fail  to  give  important  results. 

Cotton. — This  fibre  may  be  regarded  as  a  long 
tubular  compound  vegetable  cell.  It  is  1200-1500 
times  as  long  as  it  is  broad.  The  outer  sheath  is 
considered  to  be  pure  cellulose.  The  inner  layers 
are  made  up  of  secondary  cellular  deposits ;  or  are 
formed  of  a  gradual  thickening  of  the  outer  layer. 
The  extreme  end  of  the  fibre  is  closed,  that  originally 
attached  to  the  seed  is  broken  off  irregularly. 

We  have  here  a  fibre  which  from  its  natural 
constitution  may  materially  complicate  the  normal 
action  of  dyeing.  All  the  natural  fibres  are  com- 
plicated in  their  physical  formation. 

If  all  the  fibres  in  a  pound  of  cotton  were  placed 
end  on,  they  would  extend  to  2200  miles. 

Within  the  limits  of  dyeing  temperatures,  a 
dry  heat  has  little,  or  no,  influence  on  the  fibre  sub- 
stance itself.  The  material  which  makes  up  the 
purified  cotton  fibre  is  cellulose.  This  substance 
has  been  the  subject  of  a  great  deal  of  research. 
Its  ultimate  composition  is  expressed  by  the  formula : 

C6H10^5- 

In  its  purest  form,  cellulose  is  regarded  as  an 
inert  substance,  white  in  colour,  insoluble  in  all 
ordinary  reagents,  such  as  water,  alcohol,  &c.  ; 
and  the  action  of  these  solvents  on  the  fibre  is  said 
to  be  a  negative  one.  At  a  high  temperature  and 
pressure,  the  fibre  is,  in  some  respects,  altered  by 
water.  Zinc  chloride,  phosphoric  acid,  and  am- 
moniacal  copper  solution  dissolve  this  fibre.  The 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    13 

precipitate  from  these  solutions  is  called  "  regene- 
rated "  cellulose  ;  and  it  has  been  maintained  that 
the  alteration  in  its  substance  is  merely  structural. 
This  is  doubtful,  however,  for  the  capacity  of  fila- 
ments prepared  from  these  regenerated  compounds 
to  absorb  dyes  is  profoundly  modified.  The  same 
phenomenon  is  noticed  with  the  regenerated  cotton 
from  an  alkaline  thiocarbonate  solution.  The  precipi- 
tated substance  is,  in  this  case,  a  hydro-cellulose  which 
also  has  an  increased  affinity  for  certain  dye-stuffs. 

Some  interesting  speculations  have  been  made  by 
A.  G.  Green  (Rev.  Gen.  des  Mat.  Col.  1904,  130)  on 
the  constitution  of  the  cellulose  molecule  (compare 
Green  and  A.  G.  Perkin,  Proc.  C.5.,  1906,  p.  136). 

The  empirical  formula  C6H10O5  is  not  sufficiently 
complex  to  explain  the  formation  of  tri-  and  penta- 
nitro-compounds.  This  investigator  considers  the 
existence  of  these  derivatives  doubtful.  The  fact 
that  cellulose  can  exist  in  the  colloid  state,  and  is 
difficultly  soluble  is  not  considered  to  indicate,  as 
previously  supposed,  a  high  molecular  weight.  The 
same  argument  is  not  used  in  the  case  of  alumina 
or  silicic  acid  to  explain  their  colloid  state. 

Many  reasons  are  given  to  justify  the  simple 
C6H10O5  formula,  and  the  original  paper  must  be 
consulted  for  the  full  details  of  this  argument. 

Faber  and  Tollens  have  obtained  from  oxycel- 
lulose  dihydroxybutyric  acid  and  isosaccharic  acid  : 
CH(OH).CH—  COOH 


CH(OH).CH—  COOH. 


14  CHEMISTRY  AND  PHYSICS  OF  DYEING 

Green  proposes  the  following  formula  for  cellu- 
lose : 

CH(OH)-CH—  CH-OH 


CH(OH)-CH— CH2. 

This  formula  brings  forward  the  aldehyde  nature 
of  cellulose  as  follows  : 

-CH-OH 


-CH2 
which  by  fixation  of  water  becomes  : 

-CH(OH)2 
-CH2(OH) 
and  then 

-CHO 
-CH2(OH). 

When  cotton  is  mercerised  we  get  an  action  of 
this  order. 

-ONa  -OH 

—  ONa  a      then,  finally  on  washing  _QJJ 

This  formula  is  also  sufficiently  complex  to 
explain  the  Fenton  reaction,  and  the  formation  of 
the  intermediate  hydration  product. 

CH  =  C 


CH  =  C. 

And  then  by  addition  of  bromine 

-CH.OH 

-CH2Br. 
And  by  elimination 

CH=C-CHO 


=  C-CH2Br. 

(w.  brom  methyl  furfural.) 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS     15 

From  the  ionic  point  of  view,  cellulose  is  regarded 
as  an  aggregate  of  ions  which  take  their  origin 
under  special  conditions  present  in  the  plant-cells 
in  which  celluloses  are  present  as  mass  aggregates. 
The  cellulose  aggregate  is,  therefore,  regarded  as  a 
mixture  of  ions  of  varying  dimensions.  As  a  con- 
sequence, cellulose  as  a  typical  colloid  has  no  definite 
reacting  unit  as  a  body  which  takes  the  crystalline 
form,  nor  a  fixed  molecular  constitution  such  as 
could  be  represented  by  a  constitutional  formula, 
the  cellulose  molecule  not  being  regarded  as  a 
static  unit  measurable  in  the  ordinary  physical  units 
so  much  as  a  dynamic  equilibrium  ;  its  reacting 
unit  at  any  moment  being  a  function  of  the  condi- 
tions under  which  it  is  placed. 

Such  is,  perhaps,  the  most  recent  definition  of 
the  constitution  of  the  celluloses  from  the  ionic 
point  of  view  as  advanced  by  C.  F.  Cross. 

If  this  view  is  accepted  as  a  working  hypothesis, 
and  we  regard  the  fibre  colloids  as  solution  aggre- 
gates rather  than  fixed  and  definite  units,  it  may  be 
taken  for  granted  that  the  further  study  of  the  action 
of  dyeing  will  throw  light  on  this  subject  generally. 

The  two  extreme  views  of  the  constitution  of 
cellulose  are  expressed  here,  and  will  indicate  to  the 
student  the  varied  nature  of  the  ideas  on  this  sub- 
ject to-day. 

Action  of  reagents  on  cotton. — Cellulose  is  unable 
to  resist  entirely  the  action  of  reagents. 

Acids,  for  instance,  may  modify  its  structure  and 
composition  in  a  remarkable  way. 


16  CHEMISTRY  AND  PHYSICS  OF  DYEING 

The  ultimate  action  of  sulphuric  acid  is  the  pro- 
duction of  grape  sugar,  but  the  action  takes  place  in 
stages  which  are  more  or  less  marked.  Dextrin 
is  an  intermediate  compound  of  the  same  ultimate 
composition  as  cellulose  itself.  The  first  action  of 
this  acid  is  of  a  less  destructive  nature.  The  cotton 
fibre  swells  up,  gelatinising  at  the  same  time.  By 
a  very  rapid  removal  of  the  strong  acid  at  this  stage, 
so-called  "  vegetable  parchment "  is  produced. 
This  product  finds  important  uses  in  the  industrial 
world.  Its  strength  is  greatly  increased  and  its  dye 
affinity  modified. 

Nitric  acid  has  a  destructive  action,  if  carried 
to  an  extreme  stage.  At  a  high  temperature  the 
acid  breaks  up  the  fibre  and  destroys  it.  The  ultimate 
products  are  different  in  this  case,  oxalic  acid  being 
one  of  the  final  products  of  the  reaction.  The  action 
of  this  acid  in  the  cold,  either  in  the  presence  of 
sulphuric  acid  or  alone  results  in  the  production  of 
nitrates.  The  higher  nitrates  being  used  as  explo- 
sives (gun-cotton),  the  lower  nitrates  dissolve  in 
solvents  such  as  ether-alcohol,  and  are  then  known 
as  collodion.  They  also  enter  into  the  composition  of 
xylonite,  &c.  The  action  of  dyes  on  these  nitrated 
fibres  is  a  more  energetic  one.  A  systematic  exam- 
ination of  their  relative  actions  on  these  different 
nitro-products  is  greatly  needed,  and  has  never  been 
published.  The  solubility  of  these  nitro-compounds 
is  entirely  different  to  that  of  the  original  cotton. 
As  mentioned  above  it  either  swells  up  or  dissolves  in 
alcohol-ether.  On  the  other  hand,  it  no  longer 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    17 

dissolves  in  zinc  chloride.     It  is  practically  insoluble 
at  low  temperatures  in  this  reagent. 

The  action  of  weak  acids  on  cotton  fibre  is 
roughly  indicated  in  some  experiments  by  A. 
Scheurer.  The  fibre  was  subjected  to  a  20  grm. 
solution  of  oxalic  acid ;  or  its  equivalent  in  other 
acids.  The  results  are  expressed  in  percentages. 


DIMINUTION  IN  STRENGTH  OF  FIBRE. 


Acid. 

After  4  hours 
(cold). 

After  3  days 
in  hot  air. 

After  steaming 
for  i  hour. 

Oxalic 

2-5 

25.0 

25.0 

Tartaric       .         .               .0 

5-0 

10.  0 

o.  -phosphoric       .              i.o 

1-5 

15.0 

m.  -phosphoric 

2-5 

31-5 

35-o 

p.  -phosphoric 

2-5 

35-0 

35-5 

Phosphorous 

1-5 

27.0 

28.0 

The  addition  of  such  substances  as  glucose  seems 
to  exert  a  protecting  influence  when  present  in  the 
above  solutions. 

For  example,  with  oxalic  acid  and  50  grms. 
glucose  to  the  litre,  a  protection  equivalent  to 
13  per  cent,  occurs  in  hot  air,  and  6  per  cent,  on 
steaming,  as  compared  with  the  above  figures. 

Mercer  in  his  celebrated  patent  gives  an  account 
of  the  action  of  such  acid  reagents  on  cotton,  and 
notices  the  increased  effect  of  dyes  on  the  same. 

The  action  of  hydrochloric  acid  is  also  a  severe 
one.  The  cotton  fibre  falls  to  powder,  owing  to  a 
partial,  and  uneven  solution  of  the  same.  (Stern, 

2 


i8  CHEMISTRY  AND  PHYSICS  OF  DYEING 

f.C.S.j  1904,  336.)  In  all  these  cases  the  acid  must 
be  strong.  Weak  acids  have  little,  or  no  effect,  on 
this  fibre,  so  far  as  their  subsequent  reactions  are 
concerned. 

Action  of  Acid  Salts. — Bisulphates,  or  salts  which 
are  easily  dissociated,  such  as  aluminium  chloride, 
act  on  cotton,  if  their  solutions  are  allowed  to 
concentrate  by  drying  on  the  fibre.  In  such  a  way 
cotton  is  separated  from  wool  and  silk,  and  the  latter 
recovered  and  used  again.  In  the  case  of  wool  the 
recovered  fibre  is  known  as  shoddy.  A  few  years 
ago  a  lace  effect  was  produced  in  Switzerland  by 
weaving  silk  designs  on  a  cotton  foundation  and 
subsequently  "  burning  out  "  the  latter  in  this  way. 

The  other  acid  salts  act  in  a  milder  way. 

Action  of  Alkalies. — A  strong  solution  of  caustic 
alkali  profoundly  modifies  the  properties  of  the 
cotton  fibre.  Here,  as  in  the  case  of  sulphuric  acid, 
a  shrinking  and  gelatinising  action  takes  place.  A 
sodium  compound  Na2O.C12H20O10.  is  said  to  be 
formed.  Washing  in  water  decomposes  this  com- 
pound, and  a  hydro-cellulose  remains.  Within  the 
last  few  years  an  enormous  quantity  of  cotton  has 
been  treated  in  this  way.  If  a  long  staple  cotton 
be  used,  and  the  fibre  "  stretched,"  an  increased 
gloss  is  obtained ;  in  the  case  of  artificial  silk  a  similar 
result  is  obtained  (Dreaper  and  Tompkins).  After 
mercerising  a  greatly  increased  affinity  for  some  dyes 
is  exhibited. 

The   action   of   oxidising   agents   produces   oxy- 
cellulose   which   also   exhibits   increased   attraction 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    19 

for  dyes.  When  treated  with  caustic  soda  solution 
100  grammes  of  the  fibre  disengage  heat  as  follows 
(Vignon) : 

Cellulose  .         .  .74  cals. 

Oxycellulose        .          .         1.30  cals. 

This  product  also  gives  Schiffs'  reaction  for 
aldehydes.  It  will,  therefore,  be  seen  that  although 
cellulose  is  a  comparatively  inert  body,  from  the 
dyer's  point  of  view,  yet  it  attracts  dyes  more 
readily  after  being  subjected  to  the  action  of  strong 
mineral  acids,  alkalies,  or  when  dissolved  and  pre- 
cipitated. Further  particulars  of  the  action  of  such 
reagents  may  be  found  in  the  many  papers  written 
on  this  subject,  and  in  a  monograph  by  P.  Gardner, 
from  which  the  following  details  are  taken. 

The  mercerising  action  of  caustic  alkali  solu 
tion  begins  at  10°  B.  and  increases  with  the  strength 
of  solution  up  to  35°  B.  The  temperature  should 
not  exceed  20°  C.  Gardner  considers  that  to  the 
varying  chemical  action  is  due  the  different  results 
obtained  with  different  cottons.  10  per  cent,  to 
30  per  cent,  more  dye  is  required  to  produce  the 
same  shade  after  mercerising  the  fibre. 

It  is  advantageous  to  mercerise  at  a  low  tem- 
perature ;  a  weaker  solution  of  caustic  soda  will 
produce  the  same  effect.  Lefevre  (Rev.  Gen.  des  Mat. 
Col.,  1902,  p.  i)  states  that  at  the  lower  tem- 
perature a  35°  B.  solution  will  give  a  result  equal 
to  a  50°  B.  solution  at  ordinary  temperatures ; 
but  with  this  stronger  solution  and  refrigeration 
no  advantage  is  obtained. 


20  CHEMISTRY  AND  PHYSICS  OF  DYEING 

Kurz  (ibid.  p.  i)  considers  that  it  is  advanta- 
geous to  refrigerate  with  raw  cotton,  but  that  with 
bleached  cotton  it  is  not  so  necessary. 

The  heat  developed  on  mercerising  the  latter  is 
very  small,  but  the  temperature  effect  is  more 
evident  in  the  case  of  raw  cotton,  a  rise  of  13°  C. 
to  21°  C.  being  noticed  in  this  case. 

In  the  case  of  ramie  and  linen  it  is  interesting 
to  note  that  the  action  of  mercerising  is  a  different 
one.  This  is  owing  to  the  separate  cells  in  these 
fibres  swelling  up  and  ultimately  bursting.  The 
surface  of  the  fibre  becomes  correspondingly  rough 
and  not  smooth  as  in  the  case  of  cotton. 

Interesting  results  will  probably  be  obtained 
by  further  research  on  this  fibre  and  its  relative 
dyeing  properties  under  these  conditions. 

If  the  cellulose  aggregate  or  molecule  is  an 
alcoholic  anhydride,  its  chemical  activity  might  be 
due  to  the  hydroxyl  groups.  Various  acyl  and  alkyl 
derivatives  have  been  prepared  and  their  relative 
dyeing  properties  determined  by  W.  Suida  (Monatsh. 
/.  Chem.,  1905,  26,  413).  The  results  show  that  the 
dyeing  properties  of  the  nucleus  are  not  influenced 
by  the  conversion  of  these  OH  groups  into  the  acyl 
or  alkyl  ones. 

These  results  should  be  considered  in  conjunc- 
tion with  the  results  obtained  with  nitrocellulose 
and  hydrocellulose. 

Nitration  of  the  fibre,  even  to  the  extent  of  the 
introduction  of  80  per  cent,  of  NO2  groups,  does  not 
appreciably  alter  the  visible  structure  or  breaking 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS   21 

strain    of    the    thread.      (Bronnert,    Rev.   Gen.    des 
Mat.  Col.,  1900.) 

It  has  also  been  stated  that  the  introduction 
of  80-90  per  cent,  of  acetyl  groups  into  the  cellulose 
molecule,  does  not  alter  the  original  properties  of 
the  cellulose.  (Cross,  J .S.C.I.,  23,  p.  297.) 

Cotton  is  stated  to  act  energetically  as  a  catalysing 
agent  (Suida,  Monatsh.  f.  Chem.,  1905,  26,  413). 
In  a  mixture  of  benzoyl  chloride  and  sodium  hydrate 
the  former  rapidly  disappears  on  agitating  the  liquid 
in  the  presence  of  cotton.  In  its  absence  this  effect 
is  not  noticed. 

The  action  which  magnesium  and  aluminium 
chlorides  exert  on  cotton  and  other  vegetable  fibres 
is  stated  to  be  due  to  hydrolysis,  owing  to  the  hydro- 
chloric acid  set  free  on  rapid  drying. 

Only  the  vegetable  fibres  dissociate  these  salts. 
On  wool  magnesium  chloride  gives  no  trace  of  free 
acid,  even  at  a  temperature  of  140°  C.  That  the 
wool  actually  takes  up  the  chloride  is  shown  as  follows. 

Cotton  cloth  and  cashmere  were  soaked  in  solu- 
tions of  magnesium  chloride  at  13°  Tw..  and  alu- 
minium chloride  at  10°  Tw.  The  samples  were 
weighed  after  squeezing  and  the  results  would  indi- 
cate that  the  chlorine,  magnesium  and  aluminium 
taken  up  by  the  fibres  were  normal.  An  exception 
was  noted  in  the  case  of  the  aluminium  salt  and 
wool ;  more  acid  than  base  being  absorbed  in  this 
case.  (Hanofsky,  Chem.  Zeit.y  56,  1897.) 

The  hydrolysing  action  of  water  is  very  marked 
at  high  temperatures,  and  under  pressure. 


22  CHEMISTRY  AND  PHYSICS  OF  DYEING 

The  fibre  may  even  be  disintegrated  with  the 
formation  of  soluble  hydration  products. 

When  cotton  is  wetted  by  water  a  certain  rise 
in  temperature  takes  place.  At  first  sight  this 
might  be  attributed  to  a  hydrating  action,  but  the 
general  results  obtained  on  wetting  inert  substances 
(finely  divided  solids)  does  not  altogether  support 
this  idea.  It  has  long  been  known  that  a  similar 
action  takes  place  when  these  powders  are  immersed 
in  inorganic  or  organic  liquids  (Pouillet).  A  careful 
study  of  the  conditions  which  give  rise  to  these 
phenomena  has  been  made  by  Masson  (Proc.  Roy. 
Soc.,  74,  230).  Unlike  the  ordinary  disengagement 
of  heat  which  may  take  place  in  an  exothermic  reac- 
tion, there  is  no  definite  limit  either  in  time,  or  degree. 
The  action  sometimes  persists  for  hours,  giving 
an  increased  surface  temperature  of  from  8°  to  12° 
in  the  case  of  cotton.  Similar  temperature  results 
were  obtained  in  the  case  of  glass  wool  in  the  presence 
of  water  vapour.  The  conclusion  arrived  at  was 
that  the  action  is  a  distillation  effect  through  a  layer 
of  air  ;  and  that  this  gives  rise  to  the  thermal  pheno- 
mena noticed  in  these  cases.  This  investigator 
recorded  that  if  the  solid  is  wetted,  no  temperature 
effect  is  obtained  ;  and  concluded,  therefore,  that 
the  action  is  not  a  chemical  one. 

The  results  obtained  by  Martini  (Phil.  Mag.,  (5)  47, 
329)  do  not,  however,  seem  to  confirm  these  observa- 
tions. With  pure  silica,  in  a  finely  divided  state,  a 
great  rise  in  temperature  is  recorded  in  such  solutions 
as  distilled  water  (22.6°),  absolute  alcohol  (26°),  and 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    23 

sulphuric  ether  (31.5°).  Under  exceptional  circum- 
stances the  silica  was  raised  from  17°  to  80°  C.  There 
can  be  little  doubt,  but  that  the  alcohol  and  ether 
actually  wet  the  silica.  Yet  Masson  distinctly  states 
that  glass  wool  will  not  give  the  temperature  effect 
with  water,  but  only  with  water  vapour,  on  account 
of  the  air  film. 

Martini  considered  that  the  liquids  are  absorbed 
by  the  solids,  and  enter  the  solid  state  themselves 
(ibid.  (5)  50,  618).  He  subsequently  modified  this 
idea,  and  considered  the  action  a  physico-chemical 
one.  Silica  is  said  to  abstract  water  from  a  mixture 
of  three  parts  of  alcohol  to  one  of  water. 

On  the  other  hand,  he  notices  a  reverse  action 
in  the  case  when  mercury  is  the  liquid.  The  whole 
subject  seems  to  be  very  involved  in  the  present 
stage  of  our  knowledge.  Three  distinct  theories 
have  been  advanced  to  explain  the  action  depending 
on  distillation  effect ;  transfer  to  the  solid  state, 
or  a  physico-chemical  cause  respectively. 

The  matter  must  be  allowed  to  rest  here  for  the 
present,  but  the  ultimate  solution  of  this  problem 
may  possibly  throw  light  on  the  subject  of  the 
absorption  of  substances  by  fibres,  &c.,  and  is  worthy 
of  further  attention. 

The  idea  that  a  liquid  can  enter  a  solid,  and  by 
some  influence  be  degraded  to  the  solid  state,  under 
conditions  which  would  normally  determine  the 
liquid  one,  is  a  far-reaching  hypothesis.  This 
effect,  if  really  present,  must  greatly  modify  our 
ideas  on  the  attractive  value  of  fibres.  Further 


24  CHEMISTRY  AND  PHYSICS  OF  DYEING 

work  on  this  subject  is  urgently  needed,  to  clear 
up  these  points. 

Wool. — The  standard  works  must  be  referred 
to  for  details  as  to  the  actual  physical  structure  of 
the  many  varieties  which  come  upon  the  European 
markets. 

The  fibre  substance  is  called  keratine.  Its 
chemical  constitution  is  obscure.  The  published 
analyses  of  wool  vary  greatly,  and  there  is  no  direct 
evidence  that  keratine  is  a  definite  substance.  To 
prove  this,  it  is  only  necessary  to  state  that  the 
sulphur  varies  from  2  to  4  per  cent.,  and  that  this  is 
partly  removed  by  dilute  alkali.  If  strong  alkali 
is  used  the  wool  "  dissolves,"  and  if  this  solution  be 
acidified,  the  larger  part  of  the  sulphur  passes  off 
as  sulphuretted  hydrogen. 

The  mineral  matter  present,  probably  in  com- 
bination, varies  also  in  amount  (J.S.D.  and  C.,  1888, 
104)  and  composition.  It  averages  a  little  over 
i  per  cent,  on  the  weight  of  the  wool. 

The  action  of  dilute  acids  seems  to  be  more 
specific  than  in  the  case  of  the  vegetable  fibres. 
Wool  treated  with  sulphuric  acid  (or  hydrochloric) 
and  subsequently  washed  attracts  colouring-matters 
with  increased  avidity. 

Nitric  acid  gives  with  wool  a  yellow  coloura- 
tion, due  to  the  formation  of  xanthoproteic 
acid. 

Nitrous  acid  (Richard,  J.S.D.  and  C.,  1888, 
154)  "  diazotises  "  part  at  least  of  the  wool  fibre. 
Colours  can  be  "  dyed "  on  this  by  subsequent 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    25 

treatment  with  solutions  of  phenols  and  amines. 
The  writer  attempted  to  prepare  these  substances 
in  a  more  or  less  pure  state,  but  failed  chiefly  owing 
to  the  small  quantities  present.  These  "  dyes " 
are  not,  as  might  be  expected,  "  fast.'*  They  have 
little  resistance  to  the  action  of  soap  solutions  at 
the  boil  (J. S.C.I.,  1894-95).  It  is  claimed  that  the 
substance  in  the  wool  fibre  which  acts  in  this  way 
is  an  amido  acid,  termed  launginic  acid,  by  the 
discoverer  (Champion,  Compt.  Rend.,  72,  330).  To 
prepare  this  500  grm.  of  carefully  washed  wool  was 
dissolved  in  baryta  solution.  The  filtered  solution 
was  precipitated  by  lead  acetate.  After  washing 
the  lead  salt  was  suspended  in  water  and  SH2  passed 
through  the  solution.  The  filtrate  was  evaporated 
to  dryness,  yielding  about  6  per  cent,  of  a  dirty 
yellow  powder.  Champion  gives  the  formula 
C19H30N5O10  for  the  acid,  but  Knecht  and  Apple- 
yard  (J.S.D.  and  C.,  1889,  71)  do  not  agree  with 
this,  as  they  find  that  it  contains  3  per  cent,  of 
sulphur.  The  following  reactions  are  given  :  sodium 
acetate  being  present  in  the  solution. 

Alum  =  white  precipitate. 

Stannous  chloride  =  white  precipitate. 

Copper  sulphate  =  light  green  curdy  precipitate. 

Ferric  chloride  =  light  brown  precipitate. 

It  shows  the  characteristic  reaction  with  Millon's 
reagent.  A  great  number  of  lakes  have  been  pre- 
pared with  this  substance  and  the  acid  colouring- 
matters.  Schiitzenberger's  formula  for  wool  based 


26  CHEMISTRY  AND  PHYSICS  OF  DYEING 

on  its  hydrolysis  indicates  that  the  wool  molecule 
contains  the  groups 

N  =  N 

C<  and  the 


but  does  not  contain  any  NH2  groups.  Coloured 
products  would,  however,  be  obtained  as  above  by 
the  formation  of  nitrosamines  from  the  NH  group. 
The  compounds  formed  seem  to  withstand  the  action. 
The  formation  of  these  compounds  will  be  further 
discussed  in  chap.  vii.  in  the  relation  to  the  chemi- 
cal theory  of  dyeing.  It  is  considered  by  Knecht 
(J.S.D.  and  C.,  1889,  71)  that  the  presence  of  this 
amido  acid  in  the  wool  fibre  in  an  insoluble  state 
may  be  the  cause  of  the  action  of  dyeing.  As  pre- 
pared, it  precipitates  acid  and  basic  dyes,  tannic 
acid,  and  mordants. 

Very  strong  mineral  acids  dissolve  wool,  and  the 
solution  gives  precipitates  with  the  acid  colours. 

Alkalis  affect  the  wool  fibre  more  or  less.  Very 
strong  solutions  may  even  dissolve  it.  It  is  stated 
("  Manual  of  Dyeing,"  p.  43)  that  alkalis  are  not 
retained  so  tenaciously  as  acids  after  absorption 
by  the  fibres. 

The  action  of  certain  metallic  salts  in  solution  on 
wool  is  of  the  greatest  importance  from  the  practical 
point  of  view. 

Many  salts  of  iron,  chromium,  copper,  and  other 
metals  seem  to  be  decomposed  in  the  presence  of 
the  wool  substance,  and  the  oxide  or  basic  salt  is 
precipitated  on  the  wool  out  of  the  aqueous  solution. 

The  whole    subject    of    mordanting    is    a    com- 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    27 

plicated  one,  and  will  be  considered  in  chap,  iv., 
where  the  probable  nature  of  the  reactions  observed 
will  be  discussed. 

Silk.  —  The  silk  fibre  in  its  natural  state  con- 
sists of  an  inner  and  insoluble  fibre  or  filament,  making 
up  about  70  to  76  per  cent  of  the  total  weight  of  the 
fibre,  and  an  outer  coating  of  silk  gum,  or  sericine. 
This  material  is  soluble  in  caustic  alkali  solutions 
in  the  cold,  or  soap  solutions  at  the  boil.  The  fibroin 
or  silk  substance  is  then  left  in  its  final  state. 

The  composition  of  the  fibroin  is,  like  that  of  all 
albuminoids,  uncertain.     Richardson  (J  .S.C.I.  ,  1893, 
426)  considers  the  mass  formula  to  be 
C14H16(CO.OH)3.CO.OH(NH2)5 

and  considers  that  the  graphic  formula  is  of  the  fol- 

lowing order  : 

NH.O 


x  representing  a  carbon  residue. 

There  is,  however,  no  satisfactory  evidence  that 
this  residual  fibre  is  of  a  simple  nature. 

The  ultimate  analysis  of  mulberry  leaves,  silk- 
worms sericine  and  fibroin  are  as  follows  : 


Leaves. 

Worms. 

Sericine. 

Fibroin. 

C     .        .        .  -      . 

43-73 

48.1 

42.6 

48.8 

H    . 

5-9i 

7.0 

5-9 

6.23 

N     .        . 

3-32 

9.6 

16-5 

19.00 

0    .        .        .        . 

3544 

26.3 

35-0 

25.00 

Mineral  matter 

zx.6 

9.0 

— 

It  is  possible  that  the  sericine  or  silk  gum  is  a 


28  CHEMISTRY  AND  PHYSICS  OF  DYEING 

more  soluble  oxidation  product  of  the  fibroin  and 
may  possibly  be  formed  in  the  following  way  : 

C15.H23W50(5  +  H20  +  O  -  ClftH,5N408. 
Fibroin  Sericine 

Cramer  by  the  action  of  dilute  sulphuric  acid  on 
silk  gum  obtained  5  per  cent,  of  tyrosine  (hydroxy- 
phenyl-a-amido-propionic  acid). 

/OH  /CO.OH 

C6H4<          /CH<r 

XCH/         XNH, 

and  10  per  cent,  of  amido-glyceric  acid, 

COOH 


This  body  like  silk  has  a  neutral  reaction  and 
combines  with  both  acids  and  bases. 

This  body  which  has  been  called  serene  (C3H7NO3) 
is  very  similar  to  alanine  (C3H7NO2). 

By  the  action  of  nitrous  acid  the  former  gives 
glyceric  acid,  and  the  latter  lactic  acid. 

TT     COOH  r  „  /COOH 

gives     CaH4<QH 


/COOH 
C2H3^NH2        gives 

\OH  , 

glyceric  acid. 

Therefore,    serene   may   be   a   mono-amido-glyceric 
acid 

Representing  fibroin  as 
NH  -  CO 


on  saponification  with  KOH  it  would  give  : 

^NH., 
2*<CO.OK 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    29 

Some  further  work  has  been  done  on  this  sub- 
ject by  Fischer  and  Skita  (Zeit.  /.  Phys.Chem.,  1901, 
177,  and- 1902,  221). 

By  decomposing  boiled  off  silk  by  hydrochloric 
acid,  the  following  substances  were  obtained  (per 
100  pts.  of  fibroin). 

10  pts.          .  .  /3-tyrosine 

21     „            .  "...          3-alanine 

36     „         '   .  .         .            glycocoll 

i  to  1.5  pts.  .          .  /3-leucine 

,,  -  .          .  /3-phenylalanine 

Traces  of  diamino  acids  were  discovered  in  the 
products  of  hydrolysis,  and  arginine  was  recognised 
among  them.  Serine  is  also  one  of  the  decompo- 
sition products  of  fibroin  as  well  as  of  sericine. 

Sericine  yields  hydrolytic  products  from  which  a 
considerable  quantity  of  diamino-acids  may  be  sepa- 
rated by  dialysis,  arginine  being  among  them. 

These  authors  consider  that  the  difference  be- 
tween fibroin  and  sericine  is  only  a  quantitative  one. 
The  same  mono-amino  acids  are  obtained  from  both. 
In  addition  to  tyrosine  and  serine,  they  obtained 
leucine  and  phenylalanine  from  them. 

The  well-known  diazo  reaction  has  been  applied 
to  the  animal  fibres,  and  effect  colours  may  be  pro- 
duced on  silk,  by  subsequent  development  with 
phenols,  amines,  &c.  The  colours  do  not  seem,  how- 
ever, to  be  fast  to  either  washing  or  light.  The  colours 
produced  on  wool  are  duller  than  those  from  silk. 

This  matter  is  more  fully  entered  into  in  chap.  viii. 


30     *   [CHEMISTRY  AND  PHYSICS  OF  DYEING 

One  part  of  sodium  nitrite  was  found  to  be  suffi- 
cient to  "  modify  "  fifteen  parts  of  wool. 

The  resulting,  and  modified  fibre  is  very  sensitive 
to  light,  and  change  of  temperature,  like  many  of  the 
diazo  compounds.  On  boiling  with  water  it  takes 
a  brown  colour.  The  same  shade  is  produced  by 
the  action  of  dilute  sodium  hydrate  solution.  The 
alkaline  carbonates  act  in  the  same  way,  but  less 
energetically.  The  treated  wool  is  said  to  show  an 
increased  affinity  for  basic  colours  and  a  decreased 
one  for  acid  ones.  This  property  may  even  be  made 
use  of  in  printing  to  obtain  different  shades  with 
the  same  dyes. 

This  special  property  is  lost  in  sunlight.  An 
exposure  of  only  a  quarter  of  an  hour  to  diffused 
light  will  bring  the  wool  back  to  its  normal  state  so 
far  as  this  action  is  concerned. 

Nitrite  of  soda  itself,  without  the  usual  addition 
of  acid,  will  act  on  wool  at  ioo°-no°  C.  ;  a  charac- 
teristic orange-rose  colour  being  produced  under 
these  conditions  on  the  fibre. 

Many  aromatic  oxy-derivatives  will  give  colour 
effects  on  the  fibre,  in  the  same  way  as  phenols,  and 
amines,  after  treatment  with  nitrous  acid. 

Flick  and  Bourry  (Bull,  de  Soc.de  Mulh,  1889,  21) 
consider  that  this  action  is  rather  due  to  the  presence 
of  NH.  than  NH2  groups  in  the  fibre  compounds. 

The  action  of  acids  and  alkalies  on  silk  are 
therefore  in  a  way  similar  to  those  obtained  with 
wool. 

The  physical  differences  due  to  apparent  solu- 


PROPERTIES  OF  FIBRES  AND  THEIR  REACTIONS    31 

tion  may  be  noticed  when  strong  solutions  of  the 
reagents  are  used.  It  is  probable  that  hydrolysis 
takes  place,  and  that  through  this,  the  physical 
structure  is  destroyed  and  the  colloid  enters  the 
pseudo  solution  state. 

Owing  to  their  complex  nature  our  knowledge  of 
the  composition  of  the  fibre  substances  is  very 
limited,  and,  from  our  point  of  view,  unsatisfactory. 

It  is,  therefore,  difficult  to  formulate  the  relations 
of  these  bodies  to  the  dyes  and  mordants  during  the 
time  of  dyeing,  with  any  certainty,  by  arguing  from 
their  supposed  chemical  constitution.  We  must 
rather  look  for  evidence  of  a  more  indirect  nature,  to 
determine  the  reactions  between  these  animal  fibres 
and  dyestuffs  generally. 


CHAPTER  III 
DYES  AND  LAKES,  AND  THEIR  PROPERTIES 

THE  rough  division  of  dyes  into  two  groups,  the  one 
containing  the  natural  dyes,  or  those  which  are  the 
more  or  less  direct  products  of  organic  life ;  and  the 
other  the  artificial  dyes,  enables  us  to  dispose  of 
the  former  group  in  a  few  words. 

The  nature  of  these  dyes,  and  the  state  of  impurity 
in  which  they  exist  in  the  numerous  extracts,  which 
serve  in  the  ordinary  dyeing  operations,  renders  it 
very  difficult  to  discuss  their  action. 

It  may  be  stated  that  these  vegetable  dyes  are 
not  present  in  the  growing  plant.  They  exist  there 
as  chromogens,  which  are  mostly  colourless.  These 
yield  their  colouring-matters  by  subsequent  oxida- 
tion, fermentation,  &c. 

Some  of  the  products  like  indigo,  madder,  orchil, 
and  logwood  are,  or  have  been,  of  great  value  in  the 
dyeing  of  woollen  and  other  goods,  but  they  are 
being  gradually  replaced  by  new  products. 

Of  recent  years  a  good  deal  of  work  has  been 
done  on  the  constitution  of  these  dyes  when  pre- 
pared in  a  state  of  purity.  The  results  obtained  are 
hardly  of  sufficient  interest,  having  little  bearing 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     33 

on  the  action  of  dyeing,  to  claim  our  attention  in 
the  present  work. 

We  may,  therefore,  pass  on  to  the  so-called 
artificial  dyes,  the  first  of  which  was  introduced  by 
Dr.  Perkin  in  1856. 

This  dye,  mauveine,  created  a  great  sensation  at 
the  time  of  its  introduction.  In  1859,  Verquin  in- 
troduced fuchsine.  Since  that  time  the  list  has 
increased  by  ever-varying  shades  and  dyes  of  new 
constitution,  until,  to-day,  we  have  at  our  disposal 
a  range  of  colouring-matters,  which  will  respond  to 
almost  all  the  requirements  of  the  dyer,  as  regards 
fastness  and  application.  It  may  be  interesting 
here  to  review  the  different  ways  under  which  these 
dyes  have  been  classified. 

Bancroft's  scheme,  which  in  the  past  has  received 
general  acceptance,  divides  the  dyes  into  two  classes. 

(1)  Subjective. 

(2)  Adjective. 

The  first  class  includes  those  colours  which  will 
dye  without  a  mordant.  The  second  class  includes 
those  which  require  one.  In  the  present  day  it  is 
difficult  to  accept  this  simple  classification.  Some 
dyes  may  even  belong  to  both  classes. 

Von  Prager  used  the  terms  dye  and  dye-stuff 
respectively  to  describe  the  dye  materials  belonging 
to  these  two  great  classes. 

Hummel,  on  the  other  hand,  taking  note  of  the 
many  colours  which  may  be  produced  by  means  of 
different  mordants,  has  called  the  two  classes  of 
dyes  monogenetic  and  poly  genetic. 

3 


34  CHEMISTRY  AND  PHYSICS  OF  DYEING 

With  the  great  increase  in  number,  and  properties 
of  the  dyes  used  in  the  present  day,  v.  Georgievics 
has  fallen  back  on  the  divisions  which  are  generally 
accepted  as  representing  their  actions,  viz.  : 
Acid   dyes.  Vat   dyes. 

Basic   dyes.  Mordant   dyes. 

Dye  salts.  Developing  dyes. 

Sulphur    dyes.  Albumin    dyes. 

Even  this  extended  classification  has  obvious  de- 
fects. 

With  our  increasing  knowledge  a  modification 
of  O.  N.  Witt's  classification,  which  is  of  a  more 
scientific  nature,  and  depends  on  the  constitution  of 
the  dyes,  may  ultimately  be  accepted. 

This  method  divides  the  dyes  into  classes  depend- 
ing on  the  presence  of  certain  groups  from  which 
there  is  evidence  that  their  specific  characters  are 
chiefly  derived.  These  he  calls  the  chromophorous 
groups.  These  form  the  so-called  chromogens,  which 
make  up  the  root,  or  stock  substance  of  the  dye- 
stuff. 

These  chromogens  are  converted  into  dyes  by 
the  introduction  of  salt-forming  substances. 

For  instance : 

— N  =  N — is  a  chromophorous  group. 
C6H5 — N  =  N — C6H5  is  a  chromogen. 
C6H5— N  =  N— C6H4.NH9  is  a  basic  dye. 
C6H5— N  =  N— C6H4.OH~is  an  acid  dye. 

This  classification  does  not  indicate  the  action  of 
the  dye  in  detail.  In  fact,  it  would  be  very  difficult 
to  do  this. 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     35 

From  the  point  of  view  of  dyeing,  it  is  possible  that 
some  scheme  of  classification  will  be  possible  in  the 
future,  which  will  include  classes  depending  on  their 
physical  state  in  solution,  in  conjunction  with  their 
chemical  properties  (see  chap.  x.).  It  is  at  least  a 
fact  that  all  the  dyes  are  either  acid,  or  basic  in  their 
nature ;  or  contain  both  acid  and  basic  groups  at 
the  same  time. 

The  OH  and  NH2  groups  which  give  to  the  dyes 
the  acid  or  basic  properties,  are  naturally  of  the 
greatest  importance.  In  the  above  scheme,  these 
groups  are  called  auxochromes.  They  also  seem 
to  play  a  part  which  leads  to  the  production  of 
coloured  compounds. 

Another  group,  which  is  so  often  present  in  the  dye 
molecule,  is  the  sulphonic  acid  radical  (HSO3).  The 
introduction  of  this  group  into  the  molecule  is  gene- 
rally brought  about  with  the  object  of  rendering 
the  dye  more  soluble  in  water,  and  not  with  the 
object  of  producing  colour.  As  a  matter  of  fact, 
the  reverse  action  is  generally  noticed.  The  sul- 
phonic acids  of  many  dye-stuffs  are  deficient  in 
tinctorial  power  when  compared  with  the  non-sul- 
phonated  products. 

This  is  by  far  the  commonest  way  of  bringing 
the  azo  dyes  within  the  range  of  practical  solubility. 
There  are,  however,  other  methods  of  arriving  at  the 
same  result.  Geigy  states  that  the  introduction  of  a 
trialkylammonium  group  has  this  effect. 

All  azo  compounds  are  coloured,  but  all  of  them 
are  not  dyes.  Their  chief  value  is  in  the  fact  that 


36          CHEMISTRY  AND  PHYSICS  OF  DYEING 

they  are  chromophores  and  can  be  converted  into 
dyes  by  Griess'  reaction,  which  consists  in  diazotising 
the  amine  and  combining  the  product  with  phenols, 
amines,  &c. 

This  reaction  is  not,  however,  capable  of  universal 
application.  The  constitution  of  the  azo  compound 
may  determine  otherwise.  The  amidopyridines  are 
an  example ;  only  the  beta  derivative  can  be  readily 
diazotised. 

Also,  if  the  amido  groups  are  in  the  ortho  position 
as  regards  the  azo  group,  the  compound  is  incapable 
of  diazotisation. 

As  a  general  rule  a  phenol,  or  amine,  will  enter 
the  para  position  as  compared  with  another  OH, 
or  NH2  group.  If,  however,  the  para  position 
is  already  occupied  it  will  take  up  the  ortho 
position. 

If  both  the  ortho  and  para  positions  are  filled  it 
will  probably  form  no  dye-stuff. 

By  double  entrance  of  the  diazo  group  the  pro- 
duction of  tetrazo  dyes  is  effected. 

Generally  speaking  the  simpler  dyes  are  yellow 
or  greenish  in  yellow,  but  as  the  molecule  increases 
the  colour  changes  to  orange,  then  red,  violet,  or 
blue.  A  simple  example  of  this  which  is  known  to 
all  dyers  is  seen  in  the  azo  dyes  produced  from 
primuline  on  the  fibres.  It  will  be  remembered  that 
the  following  results  are  obtained : 

With  phenol,  a  golden  yellow  shade. 
With  resorcinol,  an  orange  one. 
With  /3-naphthol,  a  red  one. 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     37 

Nietzki  was  the  first  to  notice  the  general  nature 
of  this  action  and  Schultze  to  confirm  it. 

The  actual  cause  of  the  production  of  colour  is 
not  understood. 

Armstrong  favours  the  idea  that  the  quinone 
structure  is  directly  connected  with  the  produc- 
tion of  colour  in  this  class  of  compounds.  The 
evidence,  however,  does  not  seem  to  be  complete  on 
this  point. 

Discussing  the  question  of  constitution  and 
colour,  Green  (/.S.C.I.,  1893,  12,  3)  has  pointed 
out  that  the  leuco-  or  reduction-compounds  of  various 
dyes  exhibit  a  striking  difference  of  behaviour  on 
exposure  to  air. 

Disregarding  those  colours  which  are  entirely 
split  up  by  reduction,  viz.,  the  azo,  nitro,  and  nitroso 
colours,  it  is  possible  by  this  action  to  classify  colours 
into  two  groups. 

(i)  Colours  whose  leuco-compounds  are  not  readily 
oxidised  on  exposure  to  air. 

(2)  Colours  whose  leuco-compounds  are  rapidly 
oxidised  on  exposure  to  air. 

Group  (i)  consists  of  the  triphenylmethane  series, 
the  phthaleins  or  pyrone  colours,  the  indophenols 
and  the  indamines. 

Group  (2)  contains  the  indigo  class,  azines, 
azonium  colours,  oxazines,  thiazines,  acridine 
colours,  the  thiazol,  quinoline  and  oxyanthra- 
quinone  colours. 

Accepting  Armstrong's  theory  that  colour  is 
due  to  the  quinonoid  structure  of  the  molecule. 


38  CHEMISTRY  AND  PHYSICS  OF  DYEING 

The  colouring-matters  of    the  first  group  may  be 
regarded  as  paraquinonoid, 


and  those  of  the  second  group  as  ortho-quinonoid. 


This  view  is  confirmed  (Proc.  Chem.  Soc.,  1890, 
222;  Armstrong,  Proc.  Chem.  Soc.,  1888,  4,  27; 
1892,  8,  101,  143,  189,  194). 

The  cause  of  some  colours  being  mordant  colours 
seems  to  have  been  determined  beyond  dispute. 

The  presence  of  OH  or  CO.OH  groups  is  essential 
to  the  production  of  these  colours.  The  position  of 
these  groups  is  also  a  matter  of  importance.  It  is 
necessary  that  the  two  hydroxyl  groups  shall  be  in 
the  ortho  position.  One  carboxyl  group  may  take 
the  place  of  one  hydroxyl  group. 

The  normal  group  may,  therefore,  be  taken  as 

°0>M" 


The  introduction  of  a  sulphonic  acid  group  into 
the  dye  molecule  has  a  disturbing  effect  on  the  forma- 
tion of  metallic  lakes. 

For  instance,  Alizarine  red  S  (powder)  is 


(i) 
(2) 
\S03Na 

The  addition  of  copper  sulphate  to  a  solution 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     39 

of  this  dye  will  not  produce  a  lake  or  precipitate. 
If,  however,  the  corresponding  barium  salt  is  produced 
by  adding  barium  chloride  to  the  solution  before  the 
addition  of  copper  salt  a  precipitate  is  obtained 
(Dreaper,  /.  S.C.I.,  12,  272). 

In  the  same  way,  Diamine  Fast  Red  F.  will  also 
give  a  lake  with  copper  sulphate  if  the  -SO3  group  is  in 
combination  with  barium  .  The  action  of  the  sulphonic 
acid  group  is  effective  in  preventing  the  lake  for- 
mation, even  although  it  is  far  removed  from  the 
lake-forming  group,  as  will  be  seen  in  this  particular 
case. 

/OH 

CH-N  -  N—  CK- 


TTT.M      xr    rw  ^ 
C6H/N  =    N—  C6H3<OH  (2 

It  is  difficult  to  explain  the  cause  of  this  action.  It 
may  be  found,  perhaps,  in  the  greater  solubility  of  the 
sulphonic  acid,  and  the  partial  neutralisation  of  this 
effect  by  formation  of  a  barium  salt. 

The  presence  of  an  amido  group  may  also  materi- 
ally interfere  with  the  formation  of  lakes,  even  if 
the  OH  groups  are  present  in  the  ortho  position. 
It  would  almost  seem  that  here  the  action  is  of  a 


different    nature,    the    acid    nature    of    the   |  _  QJJ 

groups  being  in  part  neutralised  by  the  proximity 
of  the  NH2  group. 

The  reason  why  certain  colours  are  mordant 
dyes  is  becoming  increasingly  involved. 

The  Liebermann    and  v.  Kostanecki   law  is   no 


40        ,  CHEMISTRY  AND  PHYSICS  OF  DYEING 

longer  accepted,  owing  to  our  increased  knowledge 
on  the  subject  since  the  year  1885. 

Buntrock  in  1901  was  the  first  to  throw  doubt 
on  this  law.  He  discovered  that  derivatives  of 
groups  in  the  ortho  position  would  dye  on  mordants. 
(Rev.  Gen.  des  Mat.  Col.  1901,  99.) 

In  the  same  year,  Noelting  established  the  fact 
that  bodies  like  hystazarine  and  quinizarine  (di- 
hydroxyanthraquinones,  2.  3  and  i.  4),  also  i.  3.  5.  7 
tetrahydroxyanthraquinone,  and  i.  8 -hydrodioxy- 
2.  4.  5.  7,  tetranitrochrysazine  were  also  capable 
of  being  mordant  colours. 

V.  Georgievics  in  1902  pointed  out  that  the  hydro- 
xyanthraquinones  do  not  follow  the  above  law. 

In  the  years  1887  and  1889,  v.  Kostanecki 
extended  and  enlarged  the  original  law  which  then 
stood  as  follows  : 

(1)  Nitroso-phenols  are  mordant  colours  when  in 
the  ortho  position. 

(2)  Phenolic    colours    dye     on     mordants     when 
they  contain  two  OH  groups  in  the  ortho  position. 

(3)  Orthoquinonedioximes    are    mordant    colours. 

(4)  Ortho-oximes  are  mordant  colours. 

In  the  year  1904,  Moehlau  and  Steimmig  (Rev. 
Gen.  des  Mat.  Col.  1904,  p.  360) return  to  this  subject. 
The  following  law  is  propounded.  In  an  aromatic 
hydroxyl  derivative  when  an  OH  group  is  in  a  position 
near  to  the  chromophore,  the  body  is  a  mordant  dye. 

Picric  acid  is  not  a  mordant  because  the  com- 
pounds with  metallic  oxides  are  soluble. 

But  trinitro-resorcinol 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     41 

OH 


NO, 


NO2 
OH 


NO, 


dyes  wool  on  chromium  or   iron   mordants,  shades 
which  are  very  fast  against  the  action  of  soap. 
Nitro-amido-phenol-sulphonic  acid 

OH 
NO,  /\  NH, 


S03H 

dyes  wool,  on  chromium,  iron,  or  aluminium  mor- 
dants and  the  shades  also  resist  the  action  of  soap. 
Ortho-hydroxyazo-benzene-/>-sulphonic  acid. 

OH 

N  =  N.C6H5 


SO3H 
and  nitro-phenol-sulpho-azo-/3-naphthol 

OH 

NO2  /\  — N  =  N— 

\)         OH 

S03H 
both  dye  on  these  same  mordants. 

Quinonoid  Colours. — From  the  point  of  view~of 
NOH  M  .  OH  d\ 


colour  the  group 


NQH 


. 

,  is  equivalent  to 


42  CHEMISTRY  AND  PHYSICS  OF  DYEING 

~,  OH    (2) 

ine   group  ^       analogous   in   grouping  to 

OH    (2) 
NOTT  r  V  seems  also  to  &lve  colouring-matters  the 

property  of  dyeing  on  mordants. 

Noelting  and  Trautmann  have   found  that    8- 
hydroxyquinoline  and  its  derivatives 


OH    N. 
are  mordant  colours. 

6-Methyl-5-keto-8-isonitrosoquinoline 

O 

ca, 


OH.N 
is  also  a  mordant  colour. 

In  a  further  communication  Prud'homme  (Rev. 
Gen.  des  Mat.  Col.,  1904,  p.  365)  doubts  whether  this 
rule  of  Moehlau  and  Steimmig  can  always  be  applied  ; 
they  having  themselves  pointed  out  that  the  chromo- 
phores 

— CH  ==  CH— CO  and  — CH  =  N- 

are  not  powerful  enough  to  transform  ortho  hy- 
droxyls  into  mordant  colours. 

He  also  points  out  that  Scheurer  had  previously 
shown  that  dehydrated  mordants  will  not  combine 
with  mordant  dyes. 

Quite    recently,  further    investigation    tends    to 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     43 

show  that  in  some  cases  alizarine  lakes  are 
not  chemical  compounds.  (W.  Biltz,  Ber.  1905, 

P.  41430 

From  a  study  of   their  formation,  alizarine  iron 

lakes  are  said  to  be  of  the  nature  of  chemical  com- 
pounds ;  but  Alizarine  Red  S.W.  lake  on  chromium 
oxide  is  said  to  be  formed  by  absorption. 

It  may  be  that  these  lakes  resemble  the  tannic 
acid  ones,  or  are  similar  to  Linder  and  Picton's  dye 
compounds  (Trans.  Chem.  Soc.  1905,  p.  1934), 
where  both  actions  seem  to  be  involved. 

The  formation  of  alizarine  lakes  may  be  due  to 
solid  solution,  absorption,  or  they  may  be  chemical 
compounds. 

Variations  in  the  concentration  of  solutions  of 
alizarine  dyes  in  contact  with  oxides  of  iron,  or 
chromium,  in  the  hydrogel  state,  give  interesting 
results. 

For  instance,  the  following  table,  showing  the 
effect  of  hydroxide  of  iron  on  alizarine,  is  instruc- 
tive. 

Initial  concent.  End  do.  Col.  abs.  per  grm. 

of  bath.  of  hydroxide. 

.OOO5  .  .  .OOII4  .  .  .0677 

.01       . .     .00234     . .     .134 

.02         .  .       .00242       .  .       .308 
.04         .  .       .00261       .  .       .655 

.06       . .     .0028      . .     i.oi 
.10       . .     .00326     . .     1.695 

.15  ..  .00369  ..  2.57 

In  the  case  of  Alizarine  Red  S.W.  on  chromium 
hydroxide,  the  following  results  were  obtained  : 


44 


CHEMISTRY  AND  PHYSICS  OF  DYEING 


Initial  concentration. 
.01 
.02 
.03 
•05 
•075 
.IO 

•50 


End  do. 

.00034 

.0031 

.00776 

.01876 

.0341 

•05 

•417 


No.  2. 


No.  i. 


Strength  of  solution, 

FORMATION    OF    LAKES    IN    AQUEOUS    SOLUTION. 

The  relative  nature  of  the  reactions  indicating 
chemical  action,  or  absorption,  respectively,  is  seen 
in  the  above  curves.  No.  i  indicates  chemical  ac- 
tion in  the  case  of  an  alizarine  iron  lake,  and  No.  2 
absorption  in  the  case  of  alizarine  on  chromium 
hydroxide.  The  decreased  absorption  of  alizarine 
dyes  on  a  dehydrated  mordant,  as  compared  with  the 
same  mordant  in  a  highly  gelatinised  state,  is  shown 
in  the  following  ratios  : 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES      45 

Alizarine  1/6 

Gallein   .          .          .          .          .         i/n 
Alizarine  Yellow  G.G.W.          .         1/9-5 

It  is  suggested  that  the  reason  why  alizarine  will 
not  dye  in  the  absence  of  lime  is  that  it  is  necessary 
for  the  alizarine  to  be  in  the  quinonoid  state,  and 
that  this  state  only  occurs  in  the  presence  of  alkali. 

O 


— COH=  {  \  OH 
-CO  - 


It  must  always  be  remembered,  that  the  alizarin 
aluminium  lake  may  not  be  so  insoluble  as  the  double 
calcium  one. 

To  decide  in  practice  whether  a  dye  belongs  to 
the  mordant  class  it  should  be  sufficient  to  make 
experiments  with  wool  mordanted  with  the  following 
metals:  aluminium,  iron,  chromium,  copper,  and 
tin.  The  value  of  the  mordant  dye  will,  of 
course,  depend  on  the  brilliancy  and  fastness  of  the 
shades  produced.  These  are  most  important  factors, 
especially  from  the  wool-dyer's  point  of  view. 

In  the  case  of  the  nitroso  dye  compounds  the 
ortho  position  between  the  O  and  — NOH  groups  is 
essential  to  a  mordant  dye. 

In  some  cases  dyes  which  possess  an  OH  group 
in  the  ortho  position  with  regard  to  azo  groups, 
may  possess  the  property  of  dyeing  on  mordants. 

This  action,  in  which  closer  grouping  evidently 
gives  rise  to  what  may  be  termed  a  more  concen-- 


46  CHEMISTRY  AND  PHYSICS  OF  DYEING 

trated  effect,  is  an  instructive  one.  It  gives  us  an 
insight  into  the  structure  of  the  molecule.  Closer 
grouping  seems  to  be  more  favourable  to  combined 
action.  This  is  seen  in  the  two  nitro-salicylic  acids, 
and  the  relative  acid  nature  of  the  i.  2.  3  and  1.2.5 
compounds  (/.  C.  5.,  88,  338)  respectively. 

The  typical  dye,  Congo  Red,  which  led  to  the 
discovery  of  the  series  of  dyes  which  dye  vegetable 
fibres  directly,  is  produced  from  benzidine  ;  and  hence 
this  series  of  dyes  have  sometimes  been  known  as 
the  benzidine -colours.  With  the  extension  of  this 
class,  and  from  their  varied  origin,  they  are  now 
known  generally  as  "  cotton  dyes/'  or  sometimes 
as  "  direct  dyes." 

Generally  they  are  prepared  by  diazotising  cer- 
tain bases ;  and  combining  the  products  with  amines, 
phenols,  or  their  sulphonic  acids. 

Sometimes  the  dyes  are  mixed  products.  In 
the  preparation  of  these,  advantage  is  taken  of  the 
fact  that  the  first  molecule  of  the  amine,  &c.,  is 
taken  up  at  a  greater  rate  than  the  second  one. 
In  this  way  these  mixed  products  are  easily  pre- 
pared. 

V.  Georgievics,  in  discussing  the  possible  cause 
of  the  attraction  of  the  cotton  fibre  for  these  dyes, 
has  pointed  out  that  it  cannot  be  due  to  the 
presence  of  the  diphenyl  group,  for  certain  dyes 
only  possessing  one  azo  group  are  known  to  dye 
cotton  without  a  mordant. 

The  so-called  sulphur  dyes  have  recently  become 
of  great  importance  in  cotton-dyeing,  on  account  of 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES     47 

their  fastness  and  the  ease  with  which  they  can  be 
applied. 

The  sulphur  dyes  originated  with  the  researches 
of  Croissant  and  Bretonniere  about  thirty  years  ago. 
Sawdust,  horn,  &c.,  were  fused  with  alkali  and 
sulphur.  As  a  result,  products  soluble  in  water 
were  obtained  which  were  capable  of  dyeing  yellow 
brown  shades.  This  substance  was  known  in  com- 
merce as  Cachou  de  Laval. 

To-day,  the  class  of  sulphur  dyes  is  an  extensive 
one,  and  they  are  classified  by  Pollak  as  follows  : 

(1)  Dyes  from  simple  benzene  and  naphthalene 
derivatives. 

(2)  Dyes  from  diphenylamine  derivatives. 

(3)  Dyes    from    anthraquinone    derivatives. 

(4)  Dyes    made    by    the    help  of    sodium    thio- 
sulphate. 

(5)  Dyes  made  by  the  help  of  chloride  of  sulphur. 
This  classification  is  a  rough  and  ready  one,  but 

the  chemistry  of  the  subject  is  very  involved.  The 
fact  that  it  is  almost  impossible  to  isolate  the  inter- 
mediate compounds,  which  are  formed  during  the 
manufacture  of  the  dyes,  renders  it  very  difficult  to 
follow  the  change  which  take  place.  Vidal,  Meyen- 
berg,  Green,  and  Perkin  have  attempted  to  throw 
light  on  this  most  interesting  subject.  Vidal  believes 
that  sulphide  dyes  produced  from  compounds  of 
simple  structure,  and  at  low  temperatures,  are  pro- 
bably thiazine  derivatives. 

These  sulphur  dyes  are  insoluble.  They  are 
brought  into  solution  by  dissolving  in  sodium 


4$  CHEMISTRY  AND  PHYSICS  OF  DYEING 

sulphide.  At  the  same  time,  they  are  reduced  to  their 
leuco-compounds,  so  that  subsequent  oxidation  is 
necessary  to  reproduce  the  colours  in  situ.  This 
may  be  brought  about  in  some  cases  by  simple  ex- 
posure to  the  air ;  or  in  others  by  the  use  of  oxidising 
materials,  such  as  hydrogen  peroxide. 

Instead  of  sodium  sulphide,  neutral  sodium  sul- 
phite has  been  recommended  as  a  solvent,  and  is  used 
in  conjunction  with  glucose  and  alkali,  which  serve 
to  reduce  the  dye  to  the  leuco  condition.  The 
addition  of  salt  to  the  dye-bath  greatly  increases  the 
dye  fixed.  The  other  insoluble  dyes  which  are  pro- 
duced in  the  fibres,  such  as  indigo,  or  aniline  black, 
present  interesting  problems  to  the  student. 

From  the  fact  that  they  are  produced  by  oxida- 
tion, the  dyeing  process  is  probably  of  a  physical 
nature. 

The  production  of  aniline  black  on  the  fibre  is  a 
complicated  process  from  the  chemical  point  of 
view. 

Here  again,  the  intermediate  products  are  not 
easily  isolated,  and  this  makes  it  difficult  to  follow 
the  reaction. 

The  basic  dyes  are  usually  hydrochlorides  of 
organic  bases.  The  combination  between  the  base 
and  acid  is  a  weak  one ;  entirely  different  in  its 
nature  from  that  of  the  sulphonic  acid  azo  dyes, 
are  very  stable  compounds. 

These  bases  form  lakes  with  tannic  acid,  which 
were  at  one  time  of  great  service  in  the  dyeing  of 
cotton  goods,  and  are  still  used  for  this  purpose  ; 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES    49 

and  also  in  the  production  of  lakes  for  pigment 
colours. 

Although  at  the  point  of  saturation,  these  com- 
pounds seem  to  combine  in  the  ratio  of  their 
chemical  equivalents  in  the  ordinary  sense  of  the 
word. 

Pararosaniline  hydrochloride — 

/CfiH4-NH2 


—is  a  typical  example  of  this  class  of  dye. 

It  has  also  been  more  recently  suggested  that 
in  some  cases  the  alizarine  lakes  are  absorption  com- 
pounds (see  page  43). 

Identification  of  dyes. — Of  the  many  schemes 
suggested,  only  that  recently  advanced  by  Prof. 
Green  in  conjunction  with  Messrs.  Yeoman  and 
Jones  (J.S.D.  and  C.  1905,  p.  236)  is  noticed  here. 

This  scheme,  like  the  earlier  one  proposed  in 
1893  by  the  first  of  these  investigators,  entails  the 
reduction  of  the  dyes  to  their  leuco-compounds. 

Originally  zinc  dust  was  used  as  the  reducing 
agent,  reoxidation  being  effected  by  exposure  to 
air,  or  else  by  chromic  acid. 

Nitro,  nitroso,  and  azo  compounds  were  com- 
pletely destroyed  on  reduction.  Dyestuifs  having 
an  ortho-quinonoid  structure  gave  leuco-compounds 
which  were  readily  reoxidised  by  air  to  their  original 
state.  Para-quinonoid  compounds  giving  leuco- 
compounds  required  chromic  acid  for  reoxidation, 

4 


50  CHEMISTRY  AND  PHYSICS  OF  DYEING 

Sodium  hydrosulphite  is  now  recommended  as  a 
reducing  agent  in  place  of  zinc  dust  ;  and  the  state- 
ment is  made,  that  the  leuco-compounds  formed 
remain  in  great  part  attached  to  the  fibre,  while 
washing  will  remove  the  fission  products  of  the 
azo  dyestuffs. 

A  persulphate  is  used  in  place  of  the  chromic  acid. 
The  following  general  behaviour  of  the  various 
chemical  groups  of  dyestuffs  is  noted. 


Decolourised  by  hydrosulphite. 

Not  decolourised 

Not  altered  by 

but  changed  to 
brown,  original 

Colour  restored  on 
exposure  to  air. 

Use  of  persulphate 
required  to  restore. 

Colour  not  re- 
stored by  air 
or  persulphate. 

hydrosulphite. 

colour  restored 
by  air  or  persul- 
phate. 

Azines 

Triphenyl 

Nitro-, 

Pyrone,  acri- 

Most  dyestuffs 

Oxazines 

methane  group. 

Nitroso-, 

dine,  quino- 

of  the 

Thiazines 

and  azo- 

line,  andthia- 

anthracene 

Indigo 

groups. 

zole  groups. 

group. 

Some  mem- 

bers of  anthra- 

cene group. 

Further  tests  with  other  reagents  are  given  in  the 
original  communication  with  a  complete  range  of 
colours  dyed  on  wool  and  silk. 

The  point  of  interest  is  the  way  the  leuco-com- 
pounds are  held  by  the  fibres.  Further  details 
should  be  of  value.  The  action  may  be  due  to  the 
colloidal  nature  of  these  compounds. 

The  different  rate  of  solubility  of  dyes  in  different 
solutions  is  important,  but  before  we  consider  this 
point  the  relative  solubilities  of  dyes  in  aqueous 
solution  at  varying  temperatures  is  given.  The 
results  are  stated  in  grammes  per  100  cc.  of  solution 


DYES  AND  LAKES,  AND  THEIR  PROPERTIES    51 

for   some   of  the  best    known    dyes.     (Pawlewsky, 
Chem.  Zeit.  73,  773.) 


Dye. 

20°  C. 

60°  C. 

100°  C. 

Martius  Yellow    . 

.002 

.OI 

•13 

Violet  R.     . 

-03 

.86 

27.24 

Cyanine 

.04 

.21 

1.  21 

Magenta 

.22 

1.28 

12.23 

Picric  Acid  . 

I.I4 

2.94 

9.14 

Erythrosine 

4-56 

12.7 

24.58 

The  increase  in  solubility  at  high  temperatures  is 
great  in  some  cases. 

The  relative  action  of  picric  acid  in  solvents 
has  been  studied  with  the  following  results.  (Sisley, 
Rev.  Gen.  des  Mat.  Col.  1902,  90.) 


Water 

H2S04  (.5%  sol.) 

Ether 

Toluene 

Amyl-alcohol 


i.oo 

43 
3.56 
8.60 
1.49 


In  toluene 
dichroism 


The  colour  of  the  solution  varies  greatly, 
it   is  almost    colourless,  and  possesses  a 
not  found  in  an  aqueous  solution. 

This  is  attributed  by  Marckwald  (Ber.  1900, 
1128)  to  electrica]  dissociation.  At  any  rate  a 
difference  in  molecular  state  is  indicated. 

The  following  table  shows  the  ratio  of  picric  acid 
taken  up  by  toluene  and  water  in  mixtures  of  the 
same  at  a  temperature  of  20°  C. 


CHEMISTRY  AND  PHYSICS  OF  DYEING 


I 
I 

4.02 
2.63 

I 

4.40 

I 

1.6 

I 
I 

1.24 
2.38 

I 

i-i5 

I 

1.63 

I 

0.72 

All 

in  water 

55 

SOLUTION  MIXTURE.  RATIO  TAKEN  UP. 

Solution  10  grms.  per  litre. 
100  cc.  OH,  .25    cc.  Tol. 
100  cc.    ,,     .100  cc.    ,, 
50  cc.    ,,     .100  cc.    ,, 
Solution  3  grms.  to  litre. 
100  cc.  OH2 .25    cc.  Tol. 
100  cc.    ,,     .100  cc.    „ 
50  cc.    „     .100  cc.    „ 
Solution  i  grm.  to  litre. 
100  cc.  OHj  .25  cc.    Tol. 
100  cc.    „     .100  cc.    „ 
50  cc.    „     .100  cc.    ,, 
Solution  .1  grm.  per  litre. 
100  cc.  OH3 .25    cc.  Tol. 

IOO  CC.     ,,       .100  CC.      „ 

50  cc.    „     .100  cc.    „ 

Sisley  explains  these  abnormal  results  with  dilute 
solutions  by  assuming  the  dissociation  of  picric 
acid  in  dilute  solutions  ;  this  being  complete  at  .1  grm. 
solution  strength ;  and  that  the  toluene  cannot  ex- 
tract the  colour  ion. 

Similar  results  were  obtained  with  ether  and 
amyl  alcohol  as  follows  : 

Ratio  of  OH2  to  Ether  or  Amyl  Alcohol  100  :  100. 

10  grms.  to  litre  sol.  .          I  :  1.79         . .          I  :  .209 
I  grm.     .          .          „         I  :  0.129        . .          I  :  .071 
.1  grm.     .          -        >          I  :  .01  . .          I  :  .0101 

.01  grm.  .  .      All  in  water     . .     All  in  water 

In  these  two  cases  we  have  dilution  also  interfering 
with  extraction  from  aqueous  solution.  It  might 
be  pointed  out  that  these  results  may  be  also 
explained  by  accepting  the  association  theory  of 
solution. 


CHAPTER  IV 
ACTION  AND  NATURE  OF  MORDANTS 

OUR  knowledge  of  the  action  of  fibres  on  certain 
metallic  salts  in  aqueous  solutions  is  incomplete. 
The  subject  is  one  of  great  interest  to  the  dyer. 
Many  of  the  difficulties  he  has  to  contend  with  are 
due  to  variations  in  the  mordanting  processes. 

Aluminium  mordants. — There  is  a  general  im- 
pression that  these  mordants  act  by  producing  a 
basic  salt  on  wool  and  silk  fibres  ;  a  corresponding 
amount  of  acid  remaining  in  solution. 

This  may,  or  may  not,  be  the  case  according  to 
the  varying  condition  of  solution.  Washing  in  water 
after  the  mordanting  process  is  said  to  render  the 
salt  fixed  more  basic  by  the  removal  of  acid,  or  an 
acid  salt.  The  rate  of  mordanting  may,  therefore, 
increase  with  the  basicity  of  the  solution.  This  is 
noticed  in  practice.  Many  neutral  and  stable  salts 
are  said  to  be  free  from  any  action  of  this  nature, 
and  will  not  act  as  mordants. 

The  influence  of  the  basicity  of  aluminium  salts 
on  the  actual  absorption  results  is  indicated  in  the 
following  table.  Aluminium  sulphates  were  pre- 
pared, and  solutions  containing  200  grms.  per  litre 


54  CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  the  respective  salts  were  taken.  The  fibre  was 
cotton.  (Liechti  and  Suida,  J.S.C.I.  1883,  537.) 

Composition  of  sulphate  used.  %  A12O3  taken  up. 

A12(SO4)3  +  i8HvO  (normal)         . .  12.9 

A1:(S04)-(OH)6  ..  51.0 

A14-(S04)3-(OH)4  . .  58.7 
A12-S04-(OH)4 

The  last  and  most  basic  salt  dissociated  so  rapidly, 
that  the  experiment  could  not  be  completed. 

It  will  be  seen  that  a  slight  increase  in  basicity 
over  the  last  salt  mentioned  would  produce  an  in- 
soluble compound  on  the  cotton  fibre  irrespective 
of  any  combination  with  the  cotton  fibre  itself. 
Some  of  these  salts  have  been  prepared,  and  are  in- 
soluble. These  experiments  are  not  so  complete  as 
they  might  be.  The  composition  of  the  salts  pre- 
cipitated on  the  fibre  has  not  been  ascertained. 
They  have  only  been  expressed  in  terms  of  the 
hydrate. 

The  fact  that  these  basic  salts  cannot  be  obtained 
directly  by  the  addition  of  alumina  to  the  normal 
sulphate  is  important.  There  does  not  seem  to  be 
any  tendency  for  the  solution  to  redissolve  any 
alumina  actually  precipitated  in  the  fibre. 

The  fact  that  a  salt  is  a  basic  one  is  not,  however, 
any  indication  that  it  will  act  as  a  mordant.  Basic 
chlorides  and  oxychlorides  of  alumina  can  be  pre- 
pared, yet  they  are  very  indifferent  mordants.  Very 
little  of  the  metal  can  be  fixed  on  the  cotton  fibre  by 
solutions  of  these  salts. 


ACTION  AND  NATURE  OF  MORDANTS  55 

On  the  other  hand,  the  sulphites  and  thiosulphates 
of  alumina  are  available  as  mordants. 

The  basic  thiocyanates,  and  the  acetates  and 
sulphacetates  are  of  great  value. 

In  practice,  it  is  advisable  to  supplement  the 
direct  fixing  action  of  the  fibre,  by  some  secondary 
reaction.  For  instance,  suitable  substances  may 
be  present,  which  in  themselves  form  insoluble  com- 
pounds by  loose  combination  with  the  alumina.  As 
an  alternative  process  the  mordanted  fibre  may 
be  passed  through  a  suitable  alkaline  bath.  Such 
materials  as  oil  mordants,  or  tannic  acid,  are  used 
as  a  preliminary  treatment.  Their  action  is  suf- 
ficiently clear.  The  alumina  is  sometimes  fixed  as 
arsenate,  phosphate,  or  silicate.  It  is  worthy  of  note 
that  all  these  precipitates  are  of  a  colloidal 
nature. 

Turkey  red  mordanting. — The  process  of  fixing 
alumina  on  the  cotton  fibre  assumes  fresh  importance 
from  the  fact,  that  the  mordant  must  contain  fatty 
acids  in  some  shape,  or  form. 

The  modern  method  of  dyeing  Turkey  red, 
differs  materially  from  the  older  processes  of  dyeing 
which  originated  in  the  East,  many  years  ago. 

Le  Pileur  d'Alpigny  published  an  account  of 
these  older  processes  in  1765. 

The  original  process  took  between  three  and  five 
weeks  to  complete,  and  it  is  quite  unnecessary  to 
try  and  follow  the  many  operations  entailed.  To-day 
Turkey  red  may  be  dyed  in  three  days,  or  even  less, 
using  artificial  alizarine  in  the  place  of  madder,  and 


56  CHEMISTRY  AND  PHYSICS  OF  DYEING 

soluble  oils  in  the  place  of  olive  oil,  or  other  fatty 
matters  of  a  more  or  less  obscure  nature. 

Alizarine  (dihydroxyanthraguinone),  C14H8O4, 
may  be  regarded  as  a  weak  dibasic  acid.  It  is  even 
capable  of  decomposing  sodium  acetate.  It  contains 
two  OH  groups  in  the  ortho  position. 

It  combines  with  most  of  the  metallic  oxides 
forming  insoluble  lakes.  A  serious  study  of  these 
compounds  has  been  undertaken  by  Liechti  and 
Suida  (J.S.D.  and  C.  1885,  271;  1886,  102,  120,  131, 
146)  and  the  chief  results  obtained  are  as  follows : 

Alizarine  combines  with  calcium  to  form  normal 
or  basic  alizarates  as  the  case  may  be.  At  a  high 
temperature,  or  if  a  solution  of  the  basic  alizarates 
be  heated,  the  normal  salt,  C14H6O4-Ca,  is  always 
formed. 

On  the  other  hand,  the  aluminium  lakes  are 
formed  with  great  difficulty  in  the  absence  of  calcium 
salts.  The  presence  of  ammonia  helps  the  reaction. 
Basic  aluminium  alizarates  are  formed,  and  are  more 
insoluble  than  the  normal  salt. 

In  the  production  of  a  Turkey  red  on  cotton,  it  is 
essential  that  a  compound  lake  of  aluminium  be 
formed.  A  great  many  of  these  have  been  prepared, 
varying  in  their  properties  and  reactions.  The 
normal  lake  is  (CI4H6O4)3  Al2-(CaO)-H2O/  and  is 
readily  soluble  in  ammonia. 

In  practice  the  alizarine  lake  is  a  compound  of 
alizarine,  calcium,  aluminium,  and  fatty  acids 
and  therefore  little  can  be  said  of  the  actual  com- 
position of  these  lakes  as  present  on  the  fibre. 


ACTION  AND  NATURE  OF  MORDANTS  57 

The  actual  operations  entailed  in  the  produc- 
tion of  this  colour  are  said  to  be  as  follows 
("  Manual  of  Dyeing/'  p.  558)  : 

(1)  Oiling. 

(2)  Sumacing. 

(3)  Mordanting. 

(4)  Dyeing. 

(5)  Clearing. 

(1)  To-day,  little  seems  to  be  used  for  oiling  but 
the   so-called   sulphated   oils.     These   are   probably 
sulphonic  acids.     At  any  rate,  their  usefulness  lies 
first  in  their  solubility  in  water,  and,  secondly,  in 
the  fact  that  they  are  readily  decomposed  by  steam, 
&c.     Bodies  similar  to  the  oxidation  products  pro- 
duced from  olive  and  castor  oils  in  the  older  pro- 
cesses are  said  to  be  formed  at  the  same  time.     This 
has,  however,  been  denied. 

(2)  The  object  of  sumacing  is  to  introduce  tannic 
acid  into  the  fibre  in  order  that  it  may  subsequently 
precipitate  and  hold  a  larger  proportion  of  alumina. 

(3)  The  mordanting  operations  consist  of  treating 
the  fibre  with   aluminium  salts ;   and  subsequently 
completing  the  fixation  of  the  alumina  on  the  fibre. 

(4)  The  dyeing  which  follows  these  operations  sup- 
plies the  alizarine,  and  lime  necessary.     A  minimum 
temperature  of  70°  C.  is  necessary  to  complete  the 
formation  of  the  lake. 

(5)  The   clearing    operations    are   generally    two 
soapings.     These  remove    any  impurities,  and   here 
the  formation  of  the  lake  is  also  modified. 

At   this   stage   stannous    chloride   is   sometimes 


58  CHEMISTRY  AND  PHYSICS  OF  DYEING 

added  to  give  "  fire  "  to  the  colour.  It  is  generally 
supposed  that  this  does  not  enter  the  lake,  but 
simply  acts  physically.  Tin  oleate  is  formed  which 
acts  as  a  varnish  on  the  fibre.  A  certain  propor- 
tion of  the  fatty  acids  in  the  soaping  solution  is  fixed 
on  the  fibre. 

This  roughly  represents  the  action  and  process 
of  dyeing  Turkey  red. 

Further  light  has  been  thrown  on  these  reactions 
by  Persoz  (Bull.  Soc.  Ind.  de  Mulh.  1903,  193). 
When  mordanted  cotton  is  dyed  with  2  grms.  of  10 
per  cent,  alizarine,  and  an  equivalent  quantity  of  lime 
per  litre,  a  deep  red  colour  is  produced  in  a  few 
minutes.  If  at  this  stage  the  fibre  be  washed  and 
dried,  the  shade  produced  is  a  dull  yellowish  brown. 
If  this  be  treated  with  a  fatty  acid  and  steamed,  a 
bright  red  colour  is  produced. 

If,  on  the  other  hand,  the  dyeing  is  prolonged  to 
say  one  hour,  this  brightening  action  will  not  take 
place.  These  experiments  indicate  that  there  are 
two  possible  modifications  of  the  compound  lake  of 
alizarine,  alumina,  and  lime.  The  former  can  be 
transformed  into  the  latter  by  steaming,  and  will  not 
then  develop ;  nor  can  it  be  reconverted  into  its 
first  form  by  any  known  means.  It  is,  of  course, 
just  as  easy  to  argue  that  when  the  final  and  satu- 
rated lake  is  formed  it  will  not  combine  with  the 
fatty  acids.  The  first  "  modification  "  may  simply 
be  a  compound  still  containing  aluminium  in  a 
state  capable  of  combining  with  the  fatty  acids. 
This  explains  the  object  of  having  the  fatty  acid 


ACTION  AND   NATURE  OF  MORDANTS  59 

present  before  the  mordanted  fibre  enters  the  dye 
bath.  It  is  well  known  that  the  so-called  alizarine 
reds,  which  are  dyed  with  subsequent  oiling,  are 
inferior  to  Turkey  reds  in  fastness,  and  colour  effect. 

The  chief  constituent  of  the  modern  soluble  oils 
is  said  to  be  ricinoleic  acid,  free  or  combined  with 
alkalies.  Boiling  the  oil  with  dilute  hydrochloric 
acid  decomposes  the  sulphonic  acid  compound  liber- 
ating this  acid.  (Noelting  and  Binder,  Bull.  Soc. 
Ind.  de  Mulh.  1888,  730.) 

On  the  other  hand,  the  superiority  of  soluble  oil 
prepared  from  castor  oil  over  that  from  olive  oil  is 
stated  to  be  due  to  the  fact  that  in  the  former  case 
an  acid  sulphonic  ether  of  an  unsaturated  acid  is 
present.  In  the  latter  case  we  have  the  corresponding 
derivative  of  a  saturated  acid.  This  is  held  to  in- 
dicate that  the  former  product  will  have  a  higher 
oxidising  power  and  consequently  be  a  better 
mordant  for  this  purpose.  (Benedikt  and  Ulyer, 
Monat.  Chem.  8, 208.)  Further  research  must  decide 
which  of  these  views  is  the  correct  one. 

Prepared  in  the  pure  state  the  above  ricinoleic 
acid  gives  lakes,  as  bright  as  those  prepared  with  the 
oleins. 

Purified  aluminium  ricinoleate  after  drying  is 
pulverulent.  Its  formula  is  A12O(OH)2(C18H33O3)2. 

This  compound  heated  with  water  and  alizarine 
begins  to  attract  the  colouring-matter  at  40°  C., 
It  then  melts  and  gradually  assumes  a  bright  red 
colour,  while  the  temperature  is  being  carried  up  to 
105°  C. 


60  CHEMISTRY  AND  PHYSICS  OF  DYEING 

This  would  seem  to  indicate  that  it  is  necessary 
for  the  fatty  acid  to  melt  before  it  can  enter  into 
combination.  This  lake  is  unaltered  by  boiling  soap 
solution.  Alcohol  and  ether  dissolve  this  lake  with 
difficulty,  and  then  cotton  may  be  "  dyed  "  with 
this  solution.  It  would  be  interesting  to  know 
something  of  the  fastness  of  the  colour,  dyed  in  this 
very  mechanical  way.  Fischli  (ibid.)  also  denies 
that  oxidation  takes  place  in  the  fixing  of  ricinoleic 
acid  on  the  fibre.  This  he  confirms  by  analysis. 
He  also  shows  that  mere  heating  in  dry  air  will  not 
"  develop  "  the  colour  of  the  lake,  but  if  steam  is 
present,  the  colour  develops  instantly.  Micro- 
scopical examination  shows  that  steam  favours  the 
formation  of  the  alizarine-lime-alumina-fatty-acid 
lake.  Immediately  after  the  steaming,  the  cloth 
has  a  sticky  feel  partly  due  to  the  melting  of  this 
lake.  In  this  way  it  penetrates  the  fibre.  It  is 
also  contended  that  tin,  if  present  in  the  soap  liquor, 
actually  enters  into  combination  with  the  mordant. 

One  of  the  most  extraordinary  statements  made 
in  connection  with  the  formation  of  these  lakes  is 
that  light  is  an  important  factor  in  the  formation  of 
the  fatty  mordants.  (Storck  and  Coninck,  Bull. 
Soc.  Ind.  de  Rouen,  1887,  44.)  Much  work  remains 
to  be  done  on  this  subject. 

Iron  mordants. — The  lakes  formed  with  alizarines 
are  quite  fast,  and  not  dependent  on  either  the  pre- 
sence of  lime  or  fatty  acids  for  their  colour,  although 
the  latter  greatly  aids  in  the  fixing  of  the  iron,  and 
lime  is  distinctly  beneficial. 


ACTION  AND  NATURE  OF  MORDANTS  61 

It  is  stated  that  the  iron  must  be  introduced  into 
the  cotton  fibre  in  the  ferrous  state  and  oxidised  in 
situ.  If  not,  the  colour  is  not  fast.  It  is  known  that 
many  dyes  are  much  faster  if  produced  in  situ,  but 
this  is  the  only  known  case  where  a  mordant  acts  in 
the  same  way.*  A  ferric  ferrous  compound  may  be 
produced  in  the  case  of  alizarine,  and  is  said  to  have 
the  following  constitution  (C14H6O4)3Fe2'FeO. 

The  fact  that  mordants  are  for  the  most  part 
of  a  basic  nature  was  noticed  as  early  as  the  year 
1849  by  Gonfreville.  When  cream  of  tartar  was  used 
he  considered  that  it  entered  into  the  composition  of 
the  lake,  and  in  some  way,  or  other,  prevented  the 
"  rubbing  off."  Acids  were  considered  to  lessen  the 
affinity  of  the  wool  for  the  mordant,  and  at  the  same 
time  to  increase  the  power  of  diffusion. 

Rouard  and  Thenard  {Ann.  de  Chimie,  74,  267) 
held  the  idea  that  wool  could  not  decompose  alum, 
but  simply  absorbed  it.  It  could  all  be  removed  by 
boiling  water.  The  fibre  would  decompose  cream 
of  tartar  on  boiling,  acid  being  taken  up  and  neu- 
tral tartrate  left  in  the  solution.  He  considered  that 
wool  boiled  with  tartar  and  alum  might  contain  alum, 
tartrates  of  alumina,  potash,  and  free  tartaric  acid. 

Later  on,  Chevreul  denied  that  the  alum  could  be 
washed  out  by  water,  and  Bolby  stated  that  actual 
decomposition  took  place ;  a  basic  salt  being  depo- 
sited on  the  fibre  leaving  the  solution  more  acid. 
Schiitzenberger  considered  that  wool  exerted  some 
special  attractive  force  retaining  the  alum  in  this 
*  If  the  mineral  colours  are  excepted. 


62  CHEMISTRY  AND  PHYSICS  OF  DYEING 

way.  The  idea  that  the  wool  precipitates  the  basic 
alum  by  removing  the  acid  from  the  solution  was 
first  put  forward  by  Liechti  and  Hummel.  (J. S.C.I. 
T3>  357-)  The  addition  of  organic  acids,  or  acid 
salts,  was  said  to  prevent  the  too  rapid  precipitation 
of  the  resulting  basic  salt  on  the  fibre. 

They  considered  also  that  the  appearance  of  a 
well  mordanted  wool  points  to  the  presence  of  a  salt, 
and  not  a  hydrate. 

These  authors  also  support  the  idea  that  a  salt 
is  precipitated, by  pointing  out  that  in  "single bath" 
dyeing  the  liquid  is  always  acid.  It  is  difficult, 
however,  to  see  the  connection  between  these  two 
operations .  In  the  latter  case  the  already  formed  lake 
is  present,  the  acid  playing  the  part  of  a  more  or  less 
active  solvent,  as  in  the  case  of  a  logwood-iron  lake ; 
or  else  by  directly  influencing  the  fibre  state. 

Harvey  pointed  out  in  1872  (Monit.  Sclent.  1872, 
598)  that  in  the  case  of  very  concentrated  solutions 
of  alum,  more  sulphuric  acid  than  alumina  is  ab- 
sorbed. This  has  been  recently  confirmed  by  v. 
Georgievics.  It  appears  that  with  a  24  per  cent, 
solution  of  alum,  and  a  proportion  of  water  to  fibre 
of  30 :  i,  alumina  and  sulphuric  acid  are  taken  up  in 
their  normal  proportions.  The  affinity  of  wool  for 
acid  is  stronger  in  dilute  solutions,  and  stronger  for 
the  alumina  in  strong  solutions.  The  relative 
curves  cross  each  other  at  24  per  cent. 

Although  wool  will  take  up  large  quantities  of 
sulphuric  acid  from  concentrated  solutions  of  this 
acid,  yet  in  dilute  solutions  water  plays  the  part  of 


ACTION   AND  NATURE  OF  MORDANTS  63 

a  base  just  as  it  precipitates  basic  salts  from 
solutions  of  the  heavy  metals. 

Alum  is  said  to  be  so  far  dissociated  in  solution 
that  the  whole  of  the  SO3  can  be  titrated  with 
sodium  hydroxide  using  phenol-phthalein  as  indicator 
(Carey  Lea).  It  is  also  noticed  that  wool  mordanted 
with  alum  reacts  acid ;  the  indication  is  that  the 
acid  is  present  in  the  free  state. 

Chromium  salts. — The  mordanting  of  wool  by 
bichromate  was  at  one  time  simply  regarded  as  a 
case  of  absorption,  the  bichromate  being  taken  up 
by  the  fibre.  The  idea  that  the  bichromate  splits 
up  into  a  chromate  which  remains  in  solution,  and 
chromic  acid  which  is  absorbed  by  the  fibre  is  put 
forward  by  E.  Knecht.  (J.S.D.  and  C.  1889,  186.) 
It  is  assumed  that  the  chromic  acid  combines  with 
one  of  the  fibre  constituents  to  form  an  insoluble 
chromate.  This  has  been  disputed,  it  being  held 
that  the  dissociation  of  the  salt  is  due  to  the  presence 
of  ammonia,  due  to  the  decomposition  of  the  fibre 
material  on  boiling. 

Knecht  found  that  the  ammonia  given  off  is  not 
sufficient  to  account  for  more  than  a  thousandth  part 
of  the  change.  He  also  denies  that  the  presence  of 
alkaline  salts  in  the  wool  bring  about  the  action. 
Taking  a  sample  of  wool  and  mordanting  it  after 
treatment  with  hydrochloric  acid,  he  found  the 
chromium  distributed  as  follows  : 

Total  bichromate  in  solution    .          .         .030  grm. 
Total  chromate      .          .         .          .         .112      ,, 
Chromic  acid  on  wool   • '.-.     , .          .         .057      „ 


64  CHEMISTRY  AND  PHYSICS  OF  DYEING 

He  does  not  uphold  Nietzki's  assertion  that  a 
chromate  of  chromium  is  formed  in  the  fibre.  It  is 
held  that  if  this  action,  which  is  represented  by  the 
following  equation,  took  place  serious  damage  to  the 
fibre  must  result. 

5K£rp7  +  5H,0  =  2Cr,(CrO4)3  +  icKOH  +  30, 

He  agrees  that  a  certain  amount  of  oxidation  goes 
on,  but  that  it  is  not  of  this  order. 

Whatever  the  state  of  the  chromium,  it  is 
capable  of  easy  reduction.  This  is  practised  by 
immersing  the  mordanted  wool  in  sulphurous  acid. 

The  action  of  assistants  in  chromium  mordanting 
such  as  tartaric,  oxalic,  or  sulphuric  acids  is  said  to 
be  primarily  that  of  the  liberation  of  chromic 
acid  .Tartar,  lactic  acid,  and  oxalic  acid  also  act 
as  reducers. 

It  is  necessary  that  the  mordants  shall  be  pro- 
perly fixed  on  the  fibres,  and  shall  not  be  merely 
precipitated  on  the  surface. 

The  presence  of  sulphates,  chlorides  and  other 
salts  in  the  mordanting  bath  prevents  the  dissocia- 
tion of  the  mordant  salt. 

The  state  in  which  dichromate  of  potash  is  pre- 
sent in  aqueous  solutions  has  been  studied  by 
Abegg  and  Cox  (Nature,  vol.  71,  281).  They  deter- 
mined the  proportion  of  free  chromic  acid  present  in 
solutions  of  different  strengths,  the  presence  of 
chromic  acid  being  indicated  by  the  following  reac- 
tion : 


ACTION  AND  NATURE  OF  MORDANTS  65 

Complete  dissociation  is  calculated  to  take  place  at 
a  dilution  of  1000  litres.  At  greater  concentra- 
tions the  following  results  were  obtained 

At  100  litres  .  .  99% 
At  10  litres  .  »  91% 
At  i  litre  .„  .  .-  62% 

These  figures  indicate,  that  the  greater  part  of  the 
salt  is  decomposed  into  chromic  acid,  in  solutions 
corresponding  in  strength  to  those  used  in  mor- 
danting wool. 

In  the  mordanting  of  cotton,  for  alizarine,  it  has 
been  shown  that  the  presence  of  calcium  salts  as 
well  as  aluminium  salts  is  necessary. 

It  is  also  found  necessary  to  have  a  metallic 
monoxide  present  in  the  case  of  wool-dyeing  (Mohlau 
and  Steimmig).  With  pure  alumina  mordant  on 
wool,  no  lake  formation  seems  to  take  place  in  the 
absence  of  calcium,  barium,  strontium,  or  magne- 
sium compounds.  The  same  effect  is  noticed  with 
iron  mordants.  In  this  case  magnesium  gives  the 
best  results.  It  is  said  that  the  same  effect  may  be 
noticed  with  chromed  wool. 

Chromium  chloride,  and  chromium  fluoride,  are 
both  used  for  mordanting  wool.  Little  is  known 
about  the  nature  of  the  reactions  in  these  cases. 

Iron  mordants  on  cotton  and  wool  have  received 
little  attention  from  the  theoretical  point  of  view. 
The  probable  nature  of  the  reactions  may  be  taken 
to  be  of  a  simpler  nature  than  in  chromium  mor- 
danting. 

Copper  mordants. — The  results  obtained  by  these 

5 


66  CHEMISTRY  AND  PHYSICS  OF  DYEING 

mordants  in  practice  is  satisfactory,  but  little  is 
known  of  the  actions  which  take  place.  Copper 
finds  little  use  except  in  the  case  of  wool-dyeing. 
No  figures  are  available  which  indicate  in  any  way 
the  course  of  the  reaction  in  this  case.  It  may 
simply  be  a  case  of  absorption.  On  the  other  hand, 
basic  compounds  may  be  fixed  in  the  fibre ;  or  some 
chemical  action  may  even  take  place,  which  leads 
to  the  same  result. 

Other  metallic  mordants. — Little  is  known  as  to  the 
actions  involved  in  the  use  of  these  compounds. 

Some  of  them  give  satisfactory  shades,  and  leave 
little  to  be  desired  on  the  score  of  fastness,  but  beyond 
this  our  knowledge  does  not  extend. 

The  salts  of  nickel  and  titanium  are  of  interest 
in  this  connection. 

Tannic  Acid. — This  substance  is  of  the  greatest 
value  to  the  dyer  of  cotton  and  some  other  vegetable 
fibres. 

The  well-known  property  of  tannic  acid  of  form- 
ing lakes  with  basic  dyes  is  taken  advantage  of.  The 
vegetable  fibres  also  seem  to  have  an  attractive 
power  for  this  acid,  perhaps  because  of  its  colloid 
properties.  The  fact  that  antimony  tannate  gives 
faster  lakes  with  the  basic  dyes,  is  perhaps  against  any 
theory  of  direct  chemical  combination  between  the 
acid  and  the  fibre. 

O.  N.  Witt  holds  (Chem.  Zeit.,  12,  1885)  that 
in  these  lakes  there  is  no  distinct  molecular  ratio 
between  the  colour  base,  and  the  tannic  acid.  There 
seems  to  be  a  definite  saturation  point,  however, 


ACTION  AND  NATURE  OF  MORDANTS  67 

for  a  solution  of  night  blue  has  been  used  volu- 
metrically  for  the  estimation  of  tannic  acid  by  direct 
precipitation. 

These  lakes  are  soluble  in  excess  of  tannic  acid, 
and  also  in  acetic  acid.  The  latter  reaction  is  some- 
times made  use  of  in  printing,  the  acetic  acid  being 
subsequently  driven  off  by  heat. 

The  lakes  containing  antimony  are  more  resistant 
to  the  action  of  alkali. 

The  tannic  acids  are  little  used  on  wool,  and  on 
silk  they  play  the  part  of  a  dye,  rather  than  a  mor- 
dant. The  bleached  acid  has  a  use  in  the  weighting 
of  light  colours  on  this  fibre,  and  in  blacks  the 
amount  of  tannin  lake  held  by  the  silk  fibre  is  of 
an  extraordinary  nature  in  some  cases. 

The  action  of  tannic  and  gallic  acid  on  fibres 
generally  is  entered  into  more  fully  elsewhere. 

A  series  of  results  obtained  by  observing  the 
action  of  different  mordants  on  silk  both  in  the 
"raw"  and  " boiled  off "  state  are  given  byP.Heer- 
mann  (Farb.  Zeit.  3,  1903).  The  mordants  chosen 
were  basic  ferric  sulphate,  basic  chromium  chloride, 
acetate  of  alumina,  and  stannic  chloride.  The  in- 
fluence of  time  on  the  mordanting  process  is  indi- 
cated in  the  table  on  p.  68.  The  figures  given 
indicate  the  increase  of  weight  of  100  parts  of  fibre. 

It  is  unfortunate  that  these  experiments  were 
not  conducted  on  such  lines  that  the  composition 
of  the  precipitated  mordants  could  be  given. 

The  decrease  in  the  weight  of  mordant  fixed 
during  the  period  of  seven,  and  fourteen  days,  may 


68 


CHEMISTRY  AND  PHYSICS  OF  DYEING 


Q 
O 

g 
H 

Q 


w 

o 


K 


CTxCOO 


H 


H     ro   in    <M 

O"^     O      t^s     t^ 


M      CO      T}- 

ro    H     csi 


lOCOHtO 


H       H       H       H       H 


rj-Hoo     csi     N     O     C^oororo 
oo     o     Hcoc^Ho       co     c 


O      O 


mo 


. 
•§  e 


1 


ff     0 


ACTION  AND  NATURE  OF  MORDANTS 


69 


be  due  not  so  much  to  a  decrease  in  the  percentage 
of  metal  deposited,  as  to  the  same  being  in  a  more 
basic  state. 

The  influence  of  temperature  on  the  mordanting 
process  is  indicated  in  the  following  table  (Farb. 
Zeit.  8  and  9,  1903) : 

COMPARATIVE  AMOUNTS  TAKEN  UP  AT  DIFFERENT 
TEMPERATURES. 


Per  cent,  increase  of  maximum  increase. 

Actual 
increase. 

o°C. 

5° 

10° 

15° 

20° 

25° 

30° 

per  cent. 

Tin 

Raw  Silk    . 

74-5 

83-5 

86.5 

89.4 

93-3 

97-5 

IOO 

18.93 

Boiled  off  . 

100 

100 

100 

100 

100 

100 

IOO 

1  6.0- 

Iron 

Raw  Silk    . 

62.6 

68.1 

77-8 

84.3 

90.3 

95-3 

IOO 

7.85 

Boiled  off  . 

100 

100 

100 

100 

100 

100 

IOO 

4-95 

Chrome 

Raw  Silk    . 

100 

100 

100 

100 

100 

IOO 

IOO 

11.38 

Boiled  off  . 

69.1 

72.9 

78.4 

86.8 

92.6 

97.2 

IOO 

5.83 

Al. 

Raw  Silk    . 

39.1 

54-5 

66.4 

84.7 

100 

IOO 

IOO 

1-43 

Boiled  off  . 

81.4 

85.6 

92.0 

95-5 

100 

IOO 

IOO 

3.12 

(Tin  and  iron  solutions  52°Tw. 


Cr.  32°Tw.     Al.  i5°Tw.; 


The  effect  of  the  condition  of  the  mordanting 
bath  as  regards  its  basicity  is  important.  Heermann 
defines  the  "  basicity  number  "  of  a  mordant  as  the 
ratio  of  absolute  acid  content  to  the  absolute  metal 
content ;  e.g.,  the  number  for  stannic  chloride  is 
4x36.45-118.5  =  1.23. 

The  influence  of  additions  of  acid  and  alkali  to 
the  normal  mordants,  star.nic  chloride,  chromium 
chloride  (basic),  Cr2Cl3(OH)3,  basic  ferric  sulphate, 
and  aluminium  acetate  is  as  follows:  the  addition 
of  alkali  in  all  cases  resulted  in  considerably  more 
mordant  being  absorbed,  but  the  addition  of  acid 
did  not  always  produce  the  opposite  effect.  With  tin 


70  CHEMISTRY  AND  PHYSICS  OF  DYEING 

and  aluminium  a  very  slight  decrease  was  noted ; 
iron,  on  the  other  hand,  showed  a  rapid  decline,  5  per 
cent,  of  acid  decreasing  the  absorption  value  to  one- 
half.  In  the  case  of  chromium  also  a  rapid  drop 
was  noticed.  That  is  to  say,  the  influence  of  acid 
on  normal  salts  is  small,  but  its  influence  on  basic 
salts  great. 

In  concluding  this  work,  Heermann  examined 
the  five  theories  which  have  been  put  forward  to 
explain  the  mordanting  process,  in  the  light  of  the 
following  facts  (Farb.  Zeit.  1904,  15,  165) : 

(1)  Nature  of  fibre  has  a  great  influence  on  the 
result. 

(2)  Mordants  cannot  be  rubbed,  or  boiled  off. 

(3)  Duration    of    treatment,    temperature,    and 
state  of  solutions,  have  great  influence  on  ultimate 
result. 

(4)  Efficiency  of  mordant  not  proportional  to  its 
ionisation. 

(5)  Temperature  of  bath  increases  during  mor- 
danting action. 

(6)  Chemically  indifferent  compounds  take  part 
in  the  process. 

(7)  Fibre  not  altered  structurally,  or  chemically 
by  the  process. 

(8)  The  basicity  of  mordant  remains   constant 
during  the  process. 

(9)  Mordant  base  on  the  fibre  is  capable  of  further 
combination  and  reaction. 

(10)  Ratio  between  weight  of  mordant  and  fibre, 
influences  the  result  of  operations. 


ACTION  AND  NATURE  OF  MORDANTS  71 

Of  the  theories  put  forward  to  explain  the  action 
of  mordanting  Heermann  prefers  the  ionic  one  to  the 
impregnation,  solution,  "  organo-metallic "  or  the 
catalytic  ones  which  are  considered  less  satisfactory. 
Light  may  be  thrown  on  this  subject  by  the  further 
study  of  the  reactions  of  substances  in  the  colloidal 
state. 


CHAPTER  V 
STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS 

THE  condition  of  the  fibres  at  the  time  of  dyeing  is 
a  most  important  factor  in  the  production  of  satis- 
factory results,  especially  where  even  dyeing  and 
fast  colours  are  required. 

It  matters  little  whether  the  action  of  dyeing  is 
of  a  physical  or  chemical  nature.  In  either  case  the 
fibre  must  be  presented  to  the  dye  solution  in  such  a 
condition,  that  an  even  and  equal  absorption  of  the 
dye-stuff  will  result.  All  parts  of  the  skein,  or  piece 
of  woven  material,  must  be  equally  acted  upon  by 
the  assistants  present  in  the  dye-bath,  when  these 
tend  to  influence  the  fibre  state. 

The  problem  of  equal  dyeing  seems  to  entail 
three  essential  factors :  (i)  The  state  or  condition  of 
the  fibre  ;  (2)  The  conditions  of  dyeing ;  (3)  The  con- 
dition of  the  dye  solution.  It  is  therefore  essential 
that  the  fibre  substance  shall  be  free  from  all  im- 
purities, natural,  or  acquired  during  the  preliminary 
processes  of  manufacture. 

Fibres  are  subjected  to  the  action  of  many  sub- 
stances, or  solutions,  with  the  object  of  attaining  this 
end. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS   73 

It  is  advisable  to  consider  the  action  of  these 
different  reagents  on  the  impurities  known  to 
be  present  in  the  natural  fibres ;  and  to  allow  for 
any  possible  action  of  these  reagents  themselves, 
on  the  purified  fibre  substances  met  with  in  com- 
merce. 

In  any  specific  case,  those  reagents  which  remove 
the  impurities,  and  leave  the  fibre  in  a  homogeneous 
state,  of  good  colour  and  lustre,  will  be  most  suitable 
for  that  special  material,  and  lead  to  satisfactory 
dyeing  results. 

It  is  hardly  necessary  to  state  that  these  condi- 
tions are  never  entirely  satisfied  in  practice.  The 
processes  in  vogue  at  the  present  time  which  make 
up  this  preliminary  treatment,  are  briefly  considered 
under  the  headings  of  the  respective  fibres. 

Silk. — This  fibre  comes  into  the  markets  in  what 
is  called  the  "  gum  "  or  raw  state. 

The  silk  fibre  or  "  boiled  off  "  silk  is  obtained  in 
a  pure  state  by  treating  the  raw  silk  with  a  hot  solu- 
tion of  some  alkali  or  soap. 

In  practice  this  is  brought  about  by  boiling  the 
silk  in  one  or  more  soap  solutions,  with  subsequent 
thorough  washing  with  soft  water. 

The  soap  solution  should  be  carefully  made  up 
with  a  neutral  soap.  A  soap  made  from  olive  oil  is 
generally  considered  to  be  a  satisfactory  one.  If  any 
free  alkali  be  present  it  must  be  in  small  quantities, 
or  the  gloss  of  the  fibre  will  suffer. 

In  these  hot  baths,  the  silk  gum  is  rapidly  re- 
moved, and  leaves  the  fibroin  in  a  suitable  condition 


74          CHEMISTRY  AND  PHYSICS  OF  DYEING 

for  the  subsequent  operations  of  mordanting  and 
dyeing. 

The  original  harshness  of  the  raw  silk  disappears, 
and  the  surface  of  the  fibroin  is  shown  in  all  its 
beauty. 

In  the  dyeing  operations  which  follow,  it  is  im- 
portant that  the  fibre  shall  be  free  from  insoluble 
soaps. 

Great  care  is  therefore  taken  to  remove  all  soap 
from  the  fibre,  and  to  protect  the  silk  against  any 
surfaces  which  might  introduce  dirt,  or  oil. 

Owing  to  the  absorptive  power  of  silk,  iron  is 
easily  taken  up  by  the  fibre,  and  this  action  must  be 
particularly  guarded  against  in  the  choice  of  dye- 
vessels,  &c. 

Although  many  substitutes  for  soap  have  been 
suggested  for  "  boiling  out  "  the  silk,  yet  in  this 
country,  at  least,  it  is  almost  universally  used. 

Such  materials  as  borax,  sodium  carbonate, 
sodium  sulphide,  and  other  weak  alkalies,  are  possible 
substitutes  for  soap  in  the  boiling-off  process,  but 
they  do  not  leave  the  silk  in  such  a  satisfactory  state, 
the  strength  and  brightness  of  the  fibre  not  being 
so  good. 

The  following  figures  indicate  the  relative  boiling- 
out  action  of  sodium  carbonate  in  distilled  water  and 
soap  solution  (5  per  cent.  sol.). 

The  time  of  boiling-out  was  a  quarter  of  an  hour, 
and  the  temperature  95°  C. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS    75 


Sam- 
ple I. 

Per  cent,  of  sodium 
carbonate. 

Per  cent,  of  Gum  removed. 

In  water. 

In  soap  sol. 

I 

.02 

7.2 

— 

2 

•05 

13-0 

— 

3 

.07 

19.1 

— 

4 

.11 

19-3 

— 

5 

.15 

19.6 

— 

6 

.0 

— 

22  j 

7 

.01 

— 

22.2 

8 

.04 

— 

22-9 

9 

.07 

— 

23.2 

10 

•15 

234 

The  use  that  the  "  boiled  off  "  liquor  is  put  to  in 
the  subsequent  process  of  dyeing  is  also  an  important 
factor  in  favour  of  the  use  of  soap.  In  the  presence 
of  the  silk  gum  the  soap  solution  may  be  acidified 
without  any  separation  of  fatty  acids.  This  emul- 
sion has  a  "  levelling  up  "  action,  and  tends  to  pre- 
vent uneven  dyeing  when  it  is  added  to  the  dye 
liquor.  The  only  other  preliminary  treatment  wh'ch 
"  boiled  off"  silk  may  be  subjected  to  is  a  bleaching 
process.  Where  the  yellow  raw  silk  is  used  this  is 
necessary  for  light  colours. 

The  operations  entailed  are  not  of  a  complicated 
nature,  but  the  action  of  the  bleaching  reagents  on 
the  composition  of  the  silk  itself  has  not  been  deter- 
mined. 

Hydrogen  peroxide  and  sulphurous  acid  are  the 
more  commonly  used  agents.  Permanganates  are 
occasionally  used,  as  also  is  nitrous  acid. 

The  silk  fibre  is  therefore  usually  presented  to  the 


76  CHEMISTRY  AND   PHYSICS  OF  DYEING 

dye  bath  in  a  hydrated,  and  slightly  alkaline  state. 
It  is  free  from  grease  or  wax.  The  efficiency  of  soap 
for  boiling  out  is  probably  due^  to  the  presence  of 
free  alkali  in  small  quantity  in  the  liquor.  Lime,  or 
magnesium  salts,  in  the  water  may  lead  to  the  forma- 
tion of  insoluble  soaps,  and  uneven  dyeing. 

The  silk  itself  may  contain  these  substances.  A 
preliminary  acid  bath  will  remove  them. 

We  know  that  alkalies  are  held  by  silk  against  the 
action  of  water  in  common  with  many  other  sub- 
stances. 

This  makes  it  difficult  to  obtain  the  boiled-out 
silk  fibre,  in  a  uniform  condition,  for  purposes  of 
investigation  and  until  further  work  has  been  done 
it  is  impossible  to  suggest  a  standard  method  of 
boiling  out  silk  for  this  purpose. 

It  is  clear  that  experiments  in  the  past  have  been 
performed  on  the  fibre,  which  has  been  treated  in 
different  ways. 

It  is  suggested  that  silk  skeins  for  special  work 
should  be  first  treated  at  95°  C.  with  a  i  per  cent, 
solution  of  olive  oil  soap,  followed  by  a  further  treat- 
ment with  \  per  cent,  solution  for  half  an  hour,  with 
subsequent  washings  in  very  weak  ammonia  (i  c.c. 
to  1000  c.c.),  and  three  or  four  washings  in  distilled 
water  at  40°  C.  This  will  give  a  fairly  pure  sample  of 
boiled-off  silk.  The  temperature  of  the  boiling- off 
solution  should  not  be  above  that  indicated. 

The  action  of  excess  of  free  alkali,  if  present  in  any 
quantity,  on  silk  or  wool,  is  decidedly  harmful.  The 
silk  itself  is  attacked  with  loss  of  strength  and  lustre. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS  77 

The  action  of  alkali  on  wool  at  high  temperatures  is 
of  a  similar  nature. 

The  effect  of  boiling  wool  for  one  hour  in  a  solu- 
tion of  alum,  acidified  with  sulphuric  acid,  causes 
considerable  hydrolysis  (Gelmo  and  Suida,  Monatsh. 
/.  Chem.  26,  855).  There  is  considerable  loss  in 
weight  and  formation  of  soluble  amino -acids.  Some 
of  the  decomposition  products  resemble  peptones 
in  their  action.  These  are  -said  to  interfere  with 
the  fastness  of  the  colours,  in  the  absence  of  mineral 
acids. 

This  breaking  down  of  the  fibre  substance  is 
accelerated  in  the  presence  of  mineral  acids.  This 
is  noticed  also  in  alkaline  solutions,  as  might  be 
expected,  with  products  of  animal  origin. 

The  action  of  caustic  soda  on  wool  is  specific 
(Washburn,  /.  5.  D.  and  C.,  1901,  261).  At  ordinary 
temperatures  wool  is  increased  in  strength  in  the 
ratio  of  55  to  41  when  soaked  in  an  82°  Tw.  solution. 
At  the  same  time  84  per  cent,  of  the  sulphur  present 
is  removed.  The  lustre  and  feel  are  said  to  be  im- 
proved, and  the  affinity  for  dyestuffs  increased. 
Treatment  with  alcoholic  potash,  with  subsequent 
slight  acidification  and  washing  is  said  also  to  give 
a  similar  result,  on  dyeing  with  direct  and  azo  dyes. 
(Gelmo  and  Suida,  ibid.} 

It  will  therefore  be  realised  that  these  preliminary 
processes  may  materially  modify  the  subsequent 
operations  of  dyeing,  &c.,  by  direct  action  on  the 
fibre  substances  themselves. 

The  processes  used  in  preparing  vegetable  fibres, 


78  CHEMISTRY  AND  PHYSICS  OF  DYEING 

by  reason  of  their  more  inert  nature,  may  be 
correspondingly  drastic. 

Of  the  preliminary  operations  in  the  treatment 
of  wool  fibre  the  objects  to  be  attained  seem  to  be 
fairly  simple.  In  the  unwashed  state  wool  consists 
of  the  fibre  proper,  which  is  protected  by  wool  fat 
and  the  suint,  or  yoke. 

I  Thoroughly  cleaned  wool  seems  to  have  the  same 
composition  as  horn,  or  feathers.  This  substance 
has  been  named  keratin.  It  is  a  proteid. 

The  wool  fat  is  peculiar  in  its  way.  It  contains 
no  glycerides.  It  is  chiefly  made  up  of  cholesterin, 
isocholesterin,  oleic,  stearic,  and  other  fatty  acids. 

The  suint  contains  about  40  per  cent,  of  inorganic 
matter.  It  chiefly  consists  of  potash  salts  of  stearic 
and  oleic  acids,  besides  phosphates,  silicates,  &c.,  in 
smaller  quantities.  The  object  of  the  preliminary 
operations  is  clearly  to  remove  these  from  the  fibre. 

The  fatty  and  wax-like  bodies  may  be  removed 
by  light  spirits,  such  as  petroleum  ether.  The  potash 
salts  may,  of  course,  be  removed  by  water. 

Soap  and  soda  are  chiefly  used  to  wash  wool.  The 
temperature  should  not  be  above  40°  C. 

The  operation  of  bleaching  wool  may  modify  its 
composition,  or  may  merely  change  the  colouring- 
matter.  The  figures  given  elsewhere  indicate  that 
the  latter  is  quite  possible. 

Sulphurous  acid  and  peroxide  of  hydrogen  are  the 
two  substances  used  for  bleaching  wool. 

The  former  may  be  used  in  the  form  of  the  gas 
(stoving),  or  else  in  aqueous  solution. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS    79 

The  basis  of  hemp,  flax,  jute,  ramie,  &c.,  is 
cellulose  more  or  less  ligaified.  Oils,  resins,  and 
colouring-matters  have  to  be  removed.  Cellulose, 
although  a  carbohydrate,  like  starch,  is  very  resistant 
to  the  action  of  ordinary  solvents,  which  may,  there- 
fore, be  used  in  the  preparation  of  these  fibres. 

Dilute  acids,  and  alkalies,  are  used  for  this  purpose. 
In  the  absence  of  air  the  action  of  the  latter  solutions 
is  reduced  to  a  minimum. 

In  the  preliminary  preparation  of  these  fibres  they 
are  submitted  to  a  retting  process.  A  series  of 
changes  brought  about  chiefly  by  bacterial  action 
takes  place.  As  a  result  the  fibre  is  freed  from  certain 
binding  substances. 

The  purified  flax  is  pure  cellulose.  Bleaching  is 
difficult  with  this  fibre,  and  dyes  are  not  so  readily 
taken  up  as  by  cotton. 

Ramie  (china  grass)  in  a  purified  state  is  cellulose, 
and  is  easily  bleached  to  a  beautiful  white  shade. 

The  general  action  of  bleaching  vegetable  fibres 
is  an  obscure  one,  and  demands  farther  attention. 

Sodium  hypochlorite  is  superior  in  many  ways  to 
the  calcium  compound.  No  tendering  of  the  fibre 
is  noticed  with  it.  This  is  probably  due  to  the  pre- 
sence of  a  smaller  quantity  of  free  hypochlorous  acid. 

The  attraction  of  cellulose  for  water  is  of  a  definite 
nature.  It  is  a  property  of  the  cellulose  substance 
itself,  and  is  independent  of  structure.  Dissolved 
and  reprecipitated  cellulose  exhibits  the  same 
phenomenon.  (Cross  and  Be  van.) 

The  hydrating  action  seems  to  be  a  function  of 


8o  CHEMISTRY  AND  PHYSICS  OF  DYEING 

the  OH  groups  in  the  cellulose  molecule.  As  they 
are  suppressed  by  combination,  so  this  property  is 
said  to  decrease. 

A  study  of  the  conditions  of  hydration  indicate 
that  the  process  is  a  continuous,  and  reversible  one. 
Cellulose  in  the  state  of  hydration  is  more  readily 
attacked  by  reagents,  and  absorbs  larger  quantities 
of  certain  dyes. 

Cross  and  Bevan  have  stated  that  cellulose  which 
has  been  artificially  dehydrated  by  alcohol  shows  a 
greater  resistance  to  reagents. 

This  hydrating  action  may  be  carried  so  far  that 
actual  solution  seems  to  take  place.  The  cellulose  is 
said  to  be  present  in  a  gelatinised  form.  (Erdmann, 
/.  Pr.  Chem.  76,  385.)  Cramer  has,  however,  shown 
that  this  conclusion  does  not  agree  with  the  osmotic 
pressure  of  the  solution.  This  is  not,  however,  a 
fatal  objection  to  this  view. 

The  action  of  alkalies  on  cellulose  at  high  tem- 
peratures has  been  examined  by  H.  Tauss  (J. S.C.I., 
1889,  913  ;  1890,  883).  Cross  and  Bevan  group  the 
celluloses  in  their  action  as  follows  : 

(a)  Those  of  maximum  resistance  to  hydrolytic 
action,  and  containing  no  directly  active  groups. 

(6)  Those  of  lesser  resistance,  and  containing 
active  CO  groups. 

(c)  Those  of  low  resistance,  i.e.,  more  or  less 
soluble  in  alkalies,  &c. 

To  the  first  class  belongs  the  typical  cellulose,  such 
as  flax,  hemp,  ramie,  &c.  The  second  class  contains 


STATE  OFj  FIBRES  AND  ACTION  OF  ASSISTANTS    81 

the  oxycelluloses,  and  the  last  class  the  non-fibrous 
celluloses. 

The  lignocelluloses  (jute)  are  unsaturated  com- 
pounds. They  form  definite  compounds  with 
chlorine.  The  action  of  jute  in  dyeing  is  noticed 
elsewhere. 

The  many  operations  which  cotton  has  to  go 
through  in  these  processes  are  partly  due  to  original 
defects,  and  partly  due  to  those  acquired  in  the  manu- 
facture (oil,  grease,  &c.).  They  include  :  boiling  in 
water,  boiling  in  lime-water  under  pressure,  treatment 
with  dilute  acid,  boiling  with  resin  soap,  bleaching, 
treatment  with  weak  acid,  thorough  washing,  and 
drying. 

The  lime  is  said  to  form  compounds  with  the  fatty 
acids ;  to  remove  certain  substances ;  and  to  act  on  the 
natural  impurities,  so  that  they  are  more  easily 
removed  by  subsequent  operations. 

The  object  of  the  next  acid  bath  will  be  obvious. 
The  effect  of  the  following  bath,  soda  lye,  is  to  remove 
fatty  acids. 

Boiling  with  this  reagent  is  said  to  be  the  essential 
process  to  render  cotton  wool  absorbent  (Kilmer, 
/.S.C.7.,  1904,  967). 

The  loss  of  weight  on  boiling  cotton  with 
caustic  soda  solution  is  indicated  in  the  following 
table. 


Loss  on  boiling  for 
Strength  of  solution.  , « 

Half-hour.  One  hour. 

I      per  cent.        4.41  per  cent.        5.71  per  cent. 
2-5         „  5-08         „  7.33 

6 


82  CHEMISTRY  AND  PHYSICS  OF  DYEING 

Resin  soap  is  added  to  the  lye-bath  when  the  cotton 
is  to  be  printed. 

The  action  of  bleaching  with  bleaching  powder, 
and  subsequent  acid  bath,  are  processes  which  bring 
about  changes  in  the  colour  of  the  impurities,  and 
to  a  certain  extent  an  oxidation  of  the  cellulose 
itself. 

The  importance  of  equal  bleaching  is  evident  from 
this  point  of  view.  The  theory  of  bleaching  has  been 
considered  by  A.  Scheurer  in  more  or  less  detail. 

The  additional  attractive  power  of  hydrated 
cellulose  (hydrocellulose)  for  dyes,  must  also  be 
considered.  This  action  has  been  noticed  by  many 
observers,  including  Schaposchnikoff  and  Minajeff 
(Zeit.  /.  Farb.  und  Text.  Ch.,  1903,  13  ;  1904,  163), 
and  Hiibner  and  Pope  (J. S.C.I.,  1904,  404).  The 
iodides  seem  to  be  capable  of  replacing  caustic  soda  in 
mercerising.  If  the  fibre  be  soaked  in  a  strong  solu- 
tion of  potassium  iodide,  and  subsequently  washed 
with  alcohol,  15  per  cent,  of  the  salt  is  retained. 
After  removing  this  with  water  the  fibre  shows  in- 
creased affinity  for  Benzopurpurine  4  B;  but  no 
increased  effect  for  basic  dyes. 

Twelve  hours  treatment  with  boiling  water  will 
also  greatly  increase  the  dyeing  effect  of  cotton  for 
4B  and  decrease  it  for  methylene  blue  (ibid.}. 

It  will  therefore  be  seen  that  the  fibres  are  very 
sensitive  to  changes  in  either  composition,  or  nature, 
when  they  are  subjected  to  the  action  of  solutions. 
Even  in  the  case  of  water  itself  this  action  is  very 
evident.  Mere  handling  will  at  once  show  that  the 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS     83 

physical  conditions  have  greatly  altered.  The  dyer 
is  most  concerned  with  the  action  of  aqueous  solu- 
tions, but  the  action  of  other  solutions  is  of  great 
interest  from  a  general  point  of  view. 

When  considering  the  action  of  different  solutions 
on  animal  fibres  during  the  process  of  dyeing,  espe- 
cially at  high  temperatures,  it  is  instructive  to  note 
their  effect  on  solutions  of  albuminoid  bodies. 

Some  albumins  may  be  salted  out  of  their  solu- 
tions by  sodium  chloride,  or  sulphate.  Others  are 
not  acted  on  by  these  reagents. 

Ammonium  sulphate  will,  however,  precipitate  or 
salt  out  nearly  all  the  proteins. 

Hollmann  considers  that  the  point  of  concentra- 
tion at  which  a  salt  begins  to  precipitate  an  albumin, 
is  just  as  characteristic  for  these  substances,  as  is  the 
point  of  saturation  in  a  crystalloid. 

Prolonged  boiling  with  dilute  acids,  or  alkalies 
decomposes  the  albumins,  forming  among  other 
substances  a  series  of  amino  acids,  including  tyrosine 
and  leucine,  and  diami.no  acids  such  as  ornithine  and 
arginine. 

So  far  as  their  reactions  with  salts  of  the  heavy 
metals  go,  they  act  like  acids,  and  form  precipitates. 

Some  albumins  are  said  to  yield  insoluble  com- 
pounds with  weak  acids,  and  may  therefore  be  said 
to  behave  like  a  base. 

They  absorb  tannic,  picric,  and  phosphotungstic 
acids  in  this  way. 

The  acidic  and  basic  properties  of  these  albumins, 
are  said  to  recall  those  of  the  pseudo  acids  and  bases. 


S4  CHEMISTRY  AND  PHYSICS  OF  DYEING 

These  reactions  are  of  interest  to  the  dyer. 
Fibres  of  animal  origin  undoubtedly  assume  the 
hydrogel  condition  on  boiling  with  water. 

From  a  study  of  the  general  reactions  we 
may  obtain  an  insight  into  the  possible  results  of 
treating  these  fibres  in  a  similar  way,  and  of 
varying  the  conditions  of  the  liquors  at  the  time 
of  dyeing. 

Very  little  real  work  has  been  done  on  the  subject 
of  the  action  of  assistants  in  dyeing  operations. 
This  subject  embraces  what  may  be  termed  the 
action  of  such  reagents  as  acids,  alkalies,  neutral  and 
acid  salts,  &c.,  on  the  absorption  of  the  dyes  by  the 
fibres,  and  on  the  fibres  themselves. 

The  nature  of  these  actions  is  in  many  cases 
obscure,  and  it  can  hardly  be  said  that  in  any  case 
it  is  fully  understood. 

From  the  practical  point  of  view,  this  study  is  of 
the  greatest  importance.  It  is  only  necessary  to 
instance  the  action  of  the  addition  of  acid  to  the  bath 
in  the  case  of  dyeing  silk,  or  wool,  with  acid  colours ; 
or  the  addition  of  salt  to  the  bath  in  the  direct  dyeing 
of  cotton  with  the  direct  cotton  dyes  to  obtain  darker 
shades. 

The  first  attempt  to  determine  the  relation 
between  acids  and  fibres  was  undertaken  by  Mills 
and  Takamine  (/.C.5.,  1883,  144). 

Their  research  on  this  subject  was  divided  into 
two  parts.  The  rate  and  amount  of  absorption  of 
individual  acids  by  silk,  wool,  and  cotton,  was  first 
determined ;  and  then  the  relative  absorption  of  the 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS     85 

acids  by  the  fibres,  when  more  than  one  acid  was 
present. 

In  the  case  where  more  than  one  acid  was  used, 
the  results  obtained  were  of  special  interest. 

For  instance  the  following  table  shows  the  results 
obtained  with  mixtures  of  sulphuric  and  hydro- 
chloric acids  with  wool  and  silk  fibres,  the  ratio  of 
absorption  being  shown. 


Proportion  of 

Wool. 

'Silk. 

H2SO4  to  HCL 

H2S04. 

HCL 

H2S04. 

HCl. 

I   to   I 

5-o 

32-5 

6.63 

.87 

I   to   2 

11.3 

25-5 

5-0 

2-5 

I   to  4 

16.56 

18.4 

4.0 

3-5 

These  figures  at  once  show  that  the  addition  of 
the  second  acid  influences  the  absorption  figure  of 
the  first  one. 

The  writer  of  this  book  has  made  an  extended 
series  of  trials  with  acids  of  varying  nature.  If 
mixtures  of  hydrochloric  acid  and,  say,  tartaric  acid 
are  used,  the  estimation  of  the  relative  absorption 
of  the  two  acids  is  an  easy  one.  The  former  acid  can 
be  estimated  in  two  ways,  viz.,  by  n/IO  sodium  car- 
bonate solution,  and  by  W/IO  silver  nitrate. 

After  allowing  for  a  certain  amount  of  hydro- 
chloric acid,  which  blank  experiments  indicate  is 
present  in  the  combined  state  in  the  solution,  the 
writer  could  not  trace  any  selective  action  of  the  fibre 
for  the  stronger  acid,  as  might  be  expected  if  the 
general  action  was  equivalent  to  any  chemical  action 


86  CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  an  ordinary  nature,  such  as  might  be  anticipated  if 
the  amino  acids  in  the  fibres  entered  into  the  reaction. 
These  figures  are  not  completed  at  the  present  time. 
Mills  and  Takamine  found  that  the  rate  of 
absorption  of  the  acids  when  present  in  the  ratio  of 
H2SO4  :  4HC1  by  wool  and  silk  is  expressed  by  the 
following  figures  : 

RATE   OF  ABSORPTION 
Fibre.  H2SO4.  HC1. 

Wool    .         .         .         100  x79-6 

Silk      »  -  .         100  175.0 

The  maximum  absorption  ratio  for  silk  and  cotton, 
on  the  other  hand,  is  given  as  follows  : 

Acid.  Cotton.  Silk. 

H2S04        .!      .  i  2.6 

HC1  .  .  I  2.2 

NaHO-       .         .  i  2.2 

In  the  case  of  wool  and  silk  the  former  takes  up 
much  more  acid,  but  they  both  absorb  about  the 
same  quantity  of  sodium  hydrate. 

When  wool  is  treated  with  weak  reagents 
separately  in  the  proportion  of  HC1  :  NaHO,  the 
absorption  is  in  the  ratio  of  2HC1  :  3NaHO. 

In  the  case  of  silk  and  cotton  the  absorptions  are 
in  each  case  sHCl :  loNaHO. 

It  is  argued  from  this  that  there  is  some  intimate 
relation  between  cotton  and  silk.  It  would  be  more 
accurate,  however,  to  assume  that  the  action  as 
represented  by  absorption  of  acids  is  a  similar  one 
in  both  cases. 

It  would  be  of  value  to  find  out  whether  the. 
relative  absorption  of  acid  and  basic  dyes,  follows 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS     87 

these   figures.     They   should   clearly    do   so   if   the 
actions  are  identical  ones. 

The  figures  for  wool,  silk  and  cotton,  therefore, 
stand  as  follows  : 

Wool  .  '   '   .-  HC1.  1.5  NaHO 

Silk    .      '    .         .  HC1.  3.3  NaHO 

Cotton        .         .  HC1.  3.3  NaHO 

The  writer  found  when  repeating  some  of  these 
results  that  in  the  case  of  silk  the  absorption  of  acid 
reaches  the  maximum  very  rapidly.  It  is  complete 
in  a  few  minutes.  After  this  no  further  alteration 
in  the  ratio  between  acid  in  solution  to  acid  in 
fibre,  took  place. 

So  far  as  the  experiments  went,  temperature  had 
little  effect  on  the  action,  but  these  matters  are 
under  investigation. 

If  the  action  of  acid,  and  alkali,  is  a  specific  one, 
depending  on  the  presence  of  ami  do  acids  in  the  fibre, 
it  must  follow  the  laws  of  ordinary  chemical  action. 
It  is  perfectly  legitimate  to  argue  from  this  action 
to  that  of  dyes,  when  comparing  their  action  on 
fibres. 

The  methods  of  estimating  the  absorption  are 
definite,  and,  so  far  as  can  be  seen,  beyond  question. 
The  following  results  obtained  with  sulphuric  acid 
solutions  and  wool  are  of  interest. 

%  Acid  employed.         %  Left  in  solution.          %  Taken  up  by  wool. 
2j  .38  2.12 

5  2.17  2.83 

10  6.37  3.63 

20  15.87  4.13 

40  35.18  4.82 


88 


CHEMISTRY  AND  PHYSICS  OF  DYEING 


These  figures  should  be  extended  ;  several  results 
should  be  shown  between  o  and  2.5  per  cent,  acid 
and  the  amount  extended  to,  say,  200  per  cent. 
There  is  a  certain  amount  of  evidence  that  there  may 
be  two  causes  of  absorption,  but  nothing  is  definite. 

Up  to  40  per  cent,  the  maximum  effect  is  not 
reached. 

Repeated  extraction  does  not  remove  all  the  acid, 
but  there  are  no  reliable  figures  on  this  subject. 

The  general  effect  will  be  better  seen  in  the 
following  curve  which  is  plotted  from  the  above 
numbers. 


20  30 

Acid  in  solution. 


40% 


ABSORPTION  OF  SULPHURIC  ACID  BY  WOOL. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS     89 

The  influence  of  time  on  the  absorption  of 
sulphuric  acid  in  the  cold  (4°C.)  is  shown  in  the  follow- 
ing curve.  (Mills  and  Takamine.) 


20  40  60  80 

Time  of  immersion. 

INFLUENCE  OF  TIME  ON  ABSORPTION  OF  ACID. 

[OH2.  250  cc.  :  Wool  2.61  grms. :  H2SO4.6625  grms.     Time  unit  £  hour.] 

Action  of  Acids  in  Dyeing.  Acid  colours. — The 
generally  accepted  theory  here  is  that  the  sodium 
salts  of  the  sulphonic  acids  are  decomposed,  and 
the  dye  acids  set  free.  This  action  certainly  takes 
place,  and  is  an  important  one,  but  from  the 
chemical  point  of  view  has  not  been  satisfactorily 
settled.  From  a  practical  point  of  view  the  excess 
of  acid  over  and  above  the  amount  required  to  set  all 
the  dye  acid  free,  seems  to  be  of  even  greater  import- 
ance. All  silk  dyers  know  that  an  excess  of  acid  in 


90  CHEMISTRY  AND  PHYSICS  OF  DYEING 

the  dye-bath  has  a  pronounced  effect  on  the  rate 
of  absorption,  and  the  amount  of  dye  absorbed. 

A  great  deal  of  work  has  yet  to  be  done  on  this 
subject.  For  instance,  starting  with  silk,  and  a  pure 
salt  of  an  acid  dye,  the  absorption  results  obtained 
by  the  addition  of  known  amounts  of  acid  should  be 
carefully  noted. 

If  the  additional  effect  is  due  to  the  greater 
affinity  of  the  fibre  for  the  free  colour  acid,  a  sudden 
difference  in  the  result  would  be  expected  at  the 
point  when  the  acid  present  is  all  set  free.  Care 
would  have  to  be  taken  to  see  that  the  added  acid 
was  not  neutralised  by  some  fibre  substance.  To  do 
this,  it  would  be  necessary  to  check  the  amount  of 
free  acid  in  the  dye  solution. 

It  must  be  acknowledged  that  the  effect  of  the 
addition  of  excess  of  acid  in  dyeing  is  obscure. 

If  we  assume  that  the  excess  of  acid  in  the  solu- 
tion is  taken  up  by  the  fibre  substance  chemically, 
we  should  expect  a  decreased  affinity  for  the  dye 
acid.  The  effect  of  the  addition  of  a  second  acid  in 
the  experiments  of  Mills  and  Takamine  shows  that 
this  is  the  result  produced  in  practice.  Increasing 
the  ratio  of  the  one  acid  to  the  other  decreases  the 
amount  of  the  second  acid  absorbed. 

The  result  obtained  with  the  colour  acids  in  the 
presence  of  excess  of  a  mineral  acid  is  of  the  opposite 
nature.  The  amount  of  the  dye  absorbed  is  increased. 
It  is  possible  that  the  acid  modifies  the  state  of  the 
fibre  either  chemically  or  otherwise,  and  that  this 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS    91 

must  be  taken  into  account,  as  well  as  possible  changes 
in  the  solution  state  of  the  dye. 

Quite  recently  some  work  has  been  done  on  this 
subject  by  Gelmo  and  Suida  (Monatsh.  f.  Chem.  26, 
855),  which  seems  directly  to  contradict  some  of  the 
previously  recorded  results. 

Using  purified  wool,  and  dyeing  with  free  colour 
acids  of  Crystal  Ponceau,  Lithol  Red,  Fast  Red  R., 
and  Alizarine  Yellow  G.G.W.,  the  intensity  of  the  re- 
sulting shade  is  said  to  be  independent  of  the  presence, 
or  absence,  of  free  mineral  acid  in  the  dye  bath. 

The  authors  consider  that  the  role  played  by  the 
excess  of  acid  is  that  of  neutralising  the  lime,  com- 
bined with  the  acid  groups  of  the  wool. 

The  writer  has  observed  that  with  silk  this  action 
can  be  directly  seen,  by  allowing  this  fibre  to  remain 
in  contact  with  deci-normal  hydrochloric  acid  solu- 
tion, and  subsequently  titrating  with  both  M/IO  alkali 
and  n/IO  silver  nitrate  solutions.  The  results  indicate 
that  all  the  hydrochloric  acid  remaining  in  the  solu- 
tion is  not  in  the  free  state.  This  complicates  the 
estimation  of  the  absorption  of  acids  by  fibres,  and 
must  be  allowed  for. 

It  has  been  noticed  that  wool  treated  with 
sulphuric  acid  and  subsequently  washed  has  a  con- 
siderably decreased  affinity  for  basic  dyes,  but  its 
affinity  for  acid  dyes  is  increased. 

If  the  wool  is  washed  with  hot  water,  and  trials 
are  made  with  alcoholic  solution  of  sulphuric  acid  it  is 
found  that  the  subsequent  absorption  of  basic  dyes 


92  CHEMISTRY  AND  PHYSICS  OF  DYEING 

is  slightly  more  in  the  case  of  hot  water  washing 
than  when  cold  water  was  used.  In  the  case  of 
aqueous  sulphuric  acid  the  reverse  action  is  noticed. 

On  the  other  hand,  the  affinity  for  acid  colours 
is  considerably  increased  after  washing  with  hot 
water,  in  the  treatment  with  sulphuric  acid,  in  either 
aqueous,  or  alcoholic  solution. 

Very  similar  results  are  obtained  with  hydro- 
chloric acid.  On  the  other  hand,  treatment  with 
acetic  acid  under  these  conditions  has  little  effect. 
The  wool  after  washing  behaves  like  the  untreated 
samples. 

On  boiling  wool  with  a  sulphuric  acid  solution  of 
alum,  considerable  hydrolysis  takes  place,  with  loss  in 
weight,  and  the  formation  of  soluble  amino  acids  is 
said  to  be  the  final  result  of  the  reaction. 

Wool  treated  with  alcoholic  zinc  chloride  (.1  per 
cent,  sol.)  and  washed  shows  a  decided  loss  in  affinity 
for  basic  dyestuffs,  and  a  greater  affinity  for  Azo- 
fuchsine  G.  (acid  colours).  This  effect  is  more 
pronounced  than  when  an  aqueous  solution  is  used. 

The  effect  of  a  preliminary  treatment  with  either 
alcoholic,  or  aqueous,  sulphuric  acid  before  mordant- 
ing is  said  to  be  as  follows.  With  chromium 
sulphate  no  appreciable  difference  is  recorded,  but 
with  aluminum  sulphate  stronger  dyeings  are  ob- 
tained. On  the  other  hand,  weaker  shades  are  pro- 
duced with  sulphate  of  iron  on  subsequent  dyeing. 

Wool  mordanted  in  this  way  also  shows  a  reduced 
affinity  for  basic  dye-stuffs,  and  an  increased  affinity 
for  acid  ones. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS    93 

Treatment  with  ammonium  carbonate  solution 
is  said  to  reverse  the  action  of  the  mordanted  fibre. 

This  secondary  effect  of  acids  is  clearly  seen  in 
some  experiments  on  the  absorption  of  fl  naphthol 
sulphonic  acid  R.  The  amount  absorbed  by  wool 
is  greatly  increased  by  the  presence  of  sulphuric  acid. 
(Hirsch,  Chem.  Zeit.  13,  432.) 

The  action  here,  if  a  chemical  one,  must  be  on  the 
wool,  and  here  again  we  might  look  for  the  opposite 
result  to  that  which  actually  takes  place.  A  careful 
study  of  this  phenomenon  is  greatly  needed. 

The  action  of  acids  in  dyeing  with  basic  colours  is 
even  more  complicated  than  in  the  case  of  acid  dyes. 

Sulphuric  acid  is  said  to  impede  the  dyeing  of 
wool  with  strongly  basic  dyes  (magenta,  methylene 
blue,  &c.),  but  to  promote  the  action  of  slightly  basic 
dyes  like  Light  Green  SF,  and  Acid  Magenta.  Hydro- 
chloric acid  acts  in  the  same  way  (Gillet,  Rev.  Gen. 
des  Mat.  Co/.,  1900,  4,  327).  The  fixing  action  of 
acids  seems  to  be  inversely  proportional  to  the 
basicity  of  the  dye-stuff. 

The  action  here  from  a  chemical  point  of  view  is 
very  obscure.  There  seem  to  be  two  possible 
explanations  of  this  action. 

(1)  That  a  more  stable  salt  is  produced  with  the 
more  strongly  basic  dyes,  and  that  consequently  the 
amount  of  base  absorbed  will  be  less. 

(2)  That  the  formation  of  basic  salts,  which  are 
insoluble,  in  the  fibre,  is  prevented ;  or  even  that  if 
the  base  itself  is  precipitated,  or  fixed,  in  the  fibre  it  is 
redissolved  in  the  presence  of  excess  of  a  strong  acid. 


94  CHEMISTRY  AND  PHYSICS  OF  DYEING 

A  weaker  acid  like  sulphurous  acid  is  said  to  have  no 
action  on  the  dyeing  of  wool. 

On  the  other  hand  Prud'homme  (Rev.  Gen.  des 
Mat.  Col.y  1898,  2,  p.  209)  gives  the  following  table 
which  indicates  that  the  opposite  is  the  effect  pro- 
duced in  practice.  The  table  shows  the  altered 
attraction  of  wool  for  dyes  after  treatment  with 
sulphur  dioxide  and  hydrogen  peroxide.  Typical 
acid  and  basic  dyes  were  taken,  and  the  maximum 
dyeing  effect  taken  as=ioo. 


Experi- 
ments. 

Treatment. 

Intensity  of  colour. 

Basic  colours. 

Acid  colours. 

I 

S02          .         .        ...        . 

50 

40 

2 

SOfandH90,  . 

100 

50 

3 

SO2  and  Na2CO3         .       - 

30 

IOO 

4 

S02  and  H902  and  Na2CO3 

80 

9° 

5 

Water  only 

20 

70 

These  figures  indicate  a  possible  cause  for  the 
results  of  uneven  bleaching  or  dyeing  in  practice. 

Assuming  that  the  wool  molecule  has  in  its 
constitution  the  group 


N-CnH2n-CO 

it  is  claimed  that  the  above  results  are  explained. 
The  treatment  would  probably  lead  to  the  formation 

of  

.OH. 


N-CnH2nCO« 


Our  knowledge  of  the  action  of  acids  is  in  a  very 
elementary   state.     The   results   recorded    are   very 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS     95 

contradictory,  and  indefinite  in  their  nature.  This  is 
specially  the  case  with  the  sulphonic  acids,  be  they 
dyes,  or  otherwise.  Green,  on  the  one  hand,  states 
that  with  the  exception  of  dehydrothiotoluidine 
sulphonic  acid  he  could  not  find  any  colourless 
sulphonic  acids  of  phenols,  or  amines,  which  had 
any  attraction  for  fibres.  On  the  other  hand,  the 
results  recorded  by  Hirsch  and  Vignon  would  indicate 
that  they  may  be  absorbed. 

It  is  probable  that  the  study  of  the  action  of 
assistants  will  do  more  than  anything  else  to  throw 
light  on  the  general  nature  of  dyeing. 

Action  of  alkalies. — Beyond  a  general  indication 
as  to  the  action  of  these  bodies  on  dyeing,  we  have 
little  knowledge. 

In  silk  dyeing,  for  instance,  it  might  be  thought 
that  they  remove  the  dye  from  the  fibre  by  forming 
an  alkaline,  and  soluble  salt.  The  fact  that  they  will 
almost  equally  well  remove  basic  dyes  is  against  this 
theory ;  and  indicates  that  the  general  action  is  not  a 
chemical  one.  They  may  act  by  increasing  the 
solubility  of  the  dye  in  the  solution,  or  by  counter- 
acting the  attraction  of  the  fibre  colloid. 

The  action  seems  to  be  a  specific  one  ;  soap, 
borax,  the  soluble  alkaline  carbonates,  ammonia,  act 
in  the  same  way,  although  they  vary  in  degree.  For 
instance,  the  relative  action  of  soap  and  sodium 
carbonate  on  ingrain  colours  and  direct  dyes  on 
silk  is  given  elsewhere ;  also  the  relative  amounts, 
of  a  series  of  primuline  dyes  taken  up  by  silk  in 
soap  solution  under  standard  conditions  where  it 


g6  CHEMISTRY  AND  PHYSICS  OF  DYEING 

seems  almost  impossible  for  the  sodium  salt  to  be 
decomposed.  The  action  of  these  substances  is  an 
important  one,  but  its  study  has  been  neglected.  The 
use  of  these  compounds  in  the  bath  itself  is  chiefly 
restricted  to  the  dyeing  of  cotton  with  the  direct 
dyes,  and  the  dyeing  of  alkaline  blue  on  wool  or 
silk. 

The  latter  example  is  an  interesting  one  from  the 
theoretical  point  of  view,  and  one  which  seems  to  have 
been  overlooked.  In  order  to  prevent  the  too  rapid 
dyeing  of  this  colour,  and  also  to  obtain  even  results, 
the  dye  is  applied  in  an  alkaline  solution.  It  is, 
therefore,  fairly  certain  that  it  is  absorbed  as  an 
alkaline  salt,  and  consequently  without  combination 
with  the  fibre  substance.  A  weak  acid  will  sub- 
sequently set  the  colour  acid  free. 

Action  of  neutral  salts. — It  is  generally  agreed  that 
the  action  of  these  compounds  in  the  dye-bath  is  of  a 
physical  nature.  It  is  assumed  that  the  decreased 
solubility  of  the  direct  dyes  in  saline  solutions  is  the 
chief  cause  of  their  action.  This  may  be  so,  but 
little  work  has  been  done  on  this  subject  to  prove  it. 
If  this  were  the  only  action,  it  is  clear  that  in  any 
solution  the  cotton  fibre  should  dry  a  darker  colour 
in  the  cold,  for  the  dye  would  be  still  more  insoluble 
under  these  conditions. 

In  practice  the  reverse  is  the  case.  The  fibre 
state  is  clearly  an  important  factor,  and  here 
temperature  is  possibly  more  important  than  the 
decreased  solubility  of  the  dye  under  any  working 
conditions. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS    97 

Under  constant  conditions  of  temperature,  &c., 
a  carefully  conducted  series  of  experiments,  dealing 
with  the  relative  solubilities  of  these  direct  dyes 
and  their  dyeing  actions  in,  say,  solutions  of  sodium 
sulphate  of  different  strengths  is  required;  also 
the  relative  actions  of  the  different  assistants  of 
this  nature,  as  compared  with  their  influence  on  the 
solubilities  of  the  dyes,  the  solubility  tests  to  be  made 
at  the  temperature  of  dyeing. 

A  series  of  figures  (W.  M.  Gardner,  Text,  Manuf., 
1890,  345)  has  been  given  indicating  the  best  pro- 
portions of  salt  to  add  to  the  bath  to  get  the  maxi- 
mum effect.  The  conditions  of  the  trials  are  of  too 
indefinite  a  nature  to  be  of  much  value  from  a  theo- 
retical point  of  view. 

The  experiments  suggested  above  might  be 
extended.  Skeins  dyed  with  colour  should  be  boiled 
with  white  skeins  in  different  saline  solutions  and 
the  relative  rates  of  diffusion  compared,  the  relative 
solubilities  under  the  conditions  of  the  experiments 
being  carefully  noted.  The  writer  hopes  to  give 
this  subject  attention. 

There  is  nothing  which  more  clearly  indicates 
the  indefinite  nature  of  our  present  knowledge  of 
the  subject  of  dyeing,  than  the  absence  of  reliable 
information  on  the  action  of  these  bodies,  especially 
when  we  consider  their  great  value,  and  general  use 
in  dyeing. 

It  is  hoped  that  before  long  these  interesting 
problems  will  be  cleared  up. 

Reference  may  be  made  to  the  experiments 

7 


98          CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  Hallitt  on  the  action  of  sodium  sulphate  in  the 
dyeing  of  wool,  which,  for  convenience,  is  noticed 
elsewhere. 

The  action  of  formaldehyde  on  the  fibre  sub- 
stances, and  the  influence  of  this  body  on  the  general 
process  of  dyeing  are  characteristic,  and  a  further 
examination  in  this  direction  is  needed. 

The  coagulating  action  of  the  substance  on 
albumin  and  gelatin  is  well  known.  In  a  similar 
way,  wool,  and  silk  fibres  are  influenced  by  this 
reagent. 

The  keratin  of  the  wool  fibre  is  rendered  less 
soluble.  Beyond  becoming  harder  the  wool  suffers 
little  from  this  treatment.  It  is  much  more  resistant 
to  change  in  the  presence  of  alkaline  liquors,  and 
steaming,  or  boiling  in  water,  has  less  disturbing 
influence  on  the  fibre. 

The  treatment  is,  therefore,  of  advantage  where 
wool  is  dyed  with  the  sulphide  dyes. 

In  the  same  way  the  silk  gum  present  in  raw  silk 
may  be  rendered  less  soluble  under  the  action  of 
alkaline  liquids,  and  soap  solution. 

This  reagent  is  used  to  fix  direct  blacks  on 
cotton.  In  this  case  the  application  follows  the 
actual  dyeing,  and  takes  place  at  a  temperature  of 
about  i6o°F. 

J.  Collingwood  (f.S.D.  and  C.,  1905,  243)  shows 
that  with  Diamine,  Columbia  and  Zambezi  Blacks 
the  effect  of  treating  in  this  way  is  to  increase  the 
fastness  to  acids  and  washing.  The  fastness  to  light 
is  not  appreciably  altered. 


STATE  OF  FIBRES  AND  ACTION  OF  ASSISTANTS   99 

The  dyeing  of  basic  colours  on  cotton  treated 
with  casein  followed  by  formaldehyde  is  of  interest. 

The  baths  are  said  to  be  exhausted,  and  the 
shades  bright  and  good. 

The  Influence  of  Temperature  on  Dye  Absorption 
is  indicated  in  the  following  curves. 


3  3 


No.  2. 


No.  i 


20°  40°  60°  8o°C. 

Temperature  of 'Solution,  'jj 

ROSANILINE  ACETATE  ON  WOOL. 

(OH2'200  cc.  :  Dye  solution  -i  grm.  per  litre  ^ 

The  reversal  in  the  absorption  of  the  dye  as 
indicated  in  the  curve  is  attributed  to  dissociation 
stress,  which  is  said  to  take  place  at  high  tempera- 
tures with  this  dye. 

Assuming  Hood's  law,  and  considering  the  absorp- 
tion as  due  to  chemical  effect,  as  well  as  the  dissocia- 
tion of  the  rosaniline  acetate,  the  combined  effect 
should  be  proportional  to  the  fourth  power  of  the 
temperature. 


ioo         CHEMISTRY  AND  PHYSICS  OF  DYEING 

The  sum  of  the  fifth  differences  being  only  —  .07, 
or  very  nearly  zero,  and  this  being  also  a  criterion  of 
a  quadratic  curve,  the  equation  of  the  curve  is 

y  =  b  (t  +  1.46)  -  c  (t  +  1.46)- -  d  (^  +  1.46)"  -r  ^+1.46)' 

when  y  is  amount  of  colour  absorbed,  t  =  tem- 
perature, and  b,  c,  d  constants  of  condition. 

A  further  set  of  experiments  similar  to  the  above 
(see  curve  2)  with  a  constant  quantity  (.0005  grm.)  in 
excess  of  dye  shows  a  double  reversal  as  indicated. 

The  results  from  this  set  of  figures  indicate  that 
at  no  practically  attainable  temperature,  near  to 
o°C.  does  colour  cease  to  be  deposited.  At  about 
39°C.  the  maximum  colour  is  deposited  (.09  per  cent.). 
At  82°  the  curve  falls  lowest  to  the  axis  of  no  colour. 

The  general  effect  of  using  an  excess  of  colour  is 
to  widen  the  range  of  temperature,  within  which 
colour  is  deposited;  to  increase  the  general  dyeing 
effects;  and  shift  the  point  of  greatest  deposition 
about  8°  upwards,  and  to  doubly  reverse  it  hereafter. 

With  mauveine  the  calculated  point  at  which  no 
colour  would  be  taken  up  is  -  23.8°C.  At  49°  there 
is  greatest  deposition  of  colour  (.08  per  cent.).  Then 
there  ensues  a  single  inflexion  in  the  curve,  and 
lastly,  the  curve  descends  rapidly  to  the  axis  of  no 
colour,  although  at  8s°C.  it  is  still  remote  therefrom. 

The  positive  disadvantage  of  dyeing  with  these 
basic  colours  at  high  temperatures  is  therefore 
apparent,  so  far  as  colour  absorption  is  concerned. 

The  absorption  of  dyes  by  wool  has  also  been 
studied  by  Brown  (J.S.D.  and  C.,  17,  92). 


STATE  OF  FIBRES  AND  ACTION  OE  ASSISTANTS  icfi 

The  dye  left  in  the  solution  on  ±00  parts  ^taikeri is 
shown  for  varying  temperatures. 


Dye. 

20° 

40° 

60° 

80° 

100° 

Acid  Magenta     . 

79 

14 

4 

4-3 

5-6 

Tartrazine 

46 

3 

i 

i 

•97 

Indigo  Carmine 

46 

3 

3-4 

3-5 

6.2 

Acid  Green 

79 

18 

4 

3-6 

5-2 

Acid  Violet  4  BW.       . 

44 

26 

20.8 

20.8 

28.7 

These  variations  are  of  interest  to  the  dyer. 
They  indicate  the  possibility  of  different  shades  being 
produced  by  a  dye  solution  containing  mixtures  of 
these  dyes  at  different  temperatures,  irrespective  of 
depth  of  shade. 

They  explain  also  why  in  wool  dyeing  the  fibre 
will  often  absorb  a  further  amount  of  dye,  if  left  to 
cool  in  the  dye  solution. 


CHAPTER  VI 
SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS 

AT  every  turn  the  dyer  is  brought  in  contact  with 
solutions  of  dyes,  mordants,  and  other  substances ; 
and  it  is  therefore  necessary  for  him  to  have  some  idea 
as  to  the  physical  state  of  substances  in  solution. 

Many  of  the  difficulties  met  with  in  the  dyehouse 
are  intimately  connected  with  the  solution  state  of 
these  materials. 

In  cases  where  the  remedies  take  the  form  of 
alteration  in  the  strength,  or  temperature  of  the  dye 
liquors ;  or  the  addition  of  third  substances  to  the 
same,  the  changes  brought  about  in  the  dyeing 
processes  are  clearly  due  to  corresponding  variations 
in  the  solutions  themselves.  Through  these  the 
absorption  of  the  dyes  may  be  modified,  and  different 
dyeing  effects  produced. 

This  subject,  generally,  is  a  complicated  and 
involved  one,  and  has  given  rise  to  much  controversy. 

A  general  clearing  up  of  our  ideas  on  the  subject 
is  urgently  needed,  in  view  of  the  importance  of  its 
influence  on  many  branches  of  physical  chemistry. 

The  solution  state  of  a  dissolved  substance  may, 
if  the  ideas  of  to-day  are  correct,  be  ascribed  to  one 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  103 

of  two  actions.     It  may  be  that  both  are  involved  in 
the  production  of  solutions. 

Stated  briefly,  the  molecules  of  the  dissolved 
substance  (solute)  are  either  in  association  with  the 
solvent  molecules ;  or  else  they  simply  migrate  in  an 
inert  solvent ,  or  medium. 

The  issue  is  therefore  clear  and  defined. 

In  the  latter  case  the  solute  is  considered  to  be 
more  or  less  in  a  state  of  dissociation,  being  split  up 
into  ions  which  also  have  the  power  of  independent 
migration  in  the  solvents,  the  cause  of  this  action 
being  unknown. 

The  two  theories  may  be  termed  the  association, 
and  dissociation  ones  respectively.  They  may  be 
said  to  include  all  the  possible  explanations  of  these 
phenomena  known  to  us  at  the  present  time. 

The  association  theory  was  primarily  based  on 
the  work  done  by  Mendeleef  on  the  isolation  of 
definite  hydrates  in  solutions.  The  work  of  Cromp- 
ton  and  Pickering  supported  this  view.  Prof. 
Armstrong  in  this  country,  and  H.  C.  Jones  in 
America,  have  advocated  this  conception  of  solu- 
tion. 

The  original  idea  of  Mendeleef  supposes,  that  a 
series  of  hydrates  are  formed  in  the  aqueous  solution ; 
and  that  these  hydrates  are  in  equilibrium  with  the 
solvent  and  with  one  another.  It  must  be  remem- 
bered that  the  presence  of  such  compounds  has  not 
been  recognised  in  the  case  of  many  other  solvents, 
but  a  number  of  hydrates  have  been  isolated  by 
crystallisation  from  aqueous  solutions  by  the  above 


104        CHEMISTRY  AND  PHYSICS  OF  DYEING 

investigators  ;  and  many  others  have  been  indicated 
by  the  alteration  in  the  physical  constants  of  the 
solutions. 

Armstrong  suggested  that  the  association  was 
only  between  the  solvent  molecules  and  the  negative 
radicle  of  the  solute  only. 

In  dealing  with  the  phenomena  of  pseudo  solution 
and  de-solution  in  dye  solutions  (J.S.C.I.,  1905, 
228),  I  ventured  to  suggest  that  the  action  might  be 
of  an  intermediate  nature,  it  being  assumed  that  the 
so-called  secondary  attraction  of  the  solvent  mole- 
cules for  those  of  the  solute  correspondingly  reduces 
the  primary  attraction  between  the  positive  and 
negative  radicles  thus  : 

(OH,),  .  .  .  H-C1  .  .  .  (OH,), 

As  a  result  the  hydrogen  and  chlorine  atoms  are 
never  entirely  beyond  the  influence  of  their  primary 
attraction  for  one  another.  Their  mutual  influence 
is  lessened,  but  not  entirely  replaced  by  the  secondary 
attraction. 

On  the  other  hand,  Dr.  Lowry  has  more  recently 
advanced  the  hypothesis  that  actual  dissociation 
may  occur  owing  to  the  formation  of  "  hydrated  " 
ions.  For  instance,  he  represents  the  solution  of 
potassium  chloride  as  follows  : 


The  solution  state,  so  far  as  the  solute  is  ionised, 
is  represented  as  split  up  into  ionic  hydrates.  The 
full  argument  in  favour  of  this  theory  is  set 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  105 

forth  in  a  recent  paper  read  before  the  Faraday 
Society. 

So  that  we  have  the  three  possible  states  of  solu- 
tion, the  ionic,  the  associated,  and  the  intermediate 
one,  which  assumes  that  the  primary  and  second- 
ary attraction  are  interchangeable  and  of  the  same 
order. 

There  is  a  further  and  alternative  hypothesis, 
which  associates  the  action  in  the  case  of  aqueous 
solution  with  the  presence  of  an  unsaturated  tervalent 
oxygen  atom. 

The  subject  is,  therefore,  narrowed  down,  so  far 
as  our  ideas  extend  at  the  present  time,  as  indicated. 
Enough  is  already  known  to  enable  us  to  judge  the 
importance  of  the  whole  subject.  It  is  impossible, 
however,  at  the  present  time  to  indicate  the  hypo- 
thesis which  will  be  ultimately  accepted  as  most 
truly  representing  the  solution  state.  In  the  mean- 
time the  dyer  cannot  fail  to  gain  information  on  the 
condition  of  his  solutions,  and  their  possible  actions, 
by  keeping  in  touch  with  the  general  principles  laid 
down  from  time  to  time  in  connection  with  this 
subject. 

It  may  be  generally  stated  that  all  substances  are 
soluble  in  water.  There  is  apparently  no  exception 
to  this  rule.  Even  such  substances  as  quartz, 
platinum,  and  gold,  are  soluble.  It  may  be  accepted 
as  a  fact,  therefore,  that  no  known  substance  is  able 
to  withstand  the  solvent  action  of  water.  The 
degree  of  solution  varies  ;  sodium  sulphate  is  very 
soluble,  barium  sulphate  is  relatively  very  insoluble. 


io6         CHEMISTRY  AND  PHYSICS  OF  DYEING 

Yet  the  solvent  action  is  there  ;  the  general  action  is 
the  same  in  both  cases. 

When,  therefore,  water  is  brought  into  contact 
with  any  substance,  fibres,  dyes,  salts,  copper  vessels, 
&c.,  solution  takes  place  in  every  case.  Although 
this  action  may  in  some  cases  be  neglected,  yet, 
under  certain  favourable  conditions  it  may  adversely 
influence  the  dyeing  results.  This  solvent  action 
may  be  greatly  modified  by  the  presence  of  third 
substances,  such  as  acids,  or  alkalies,  and  must  be 
carefully  considered. 

As  previously  stated,  the  dissociation  theory 
assumes  that  salts,  acids,  and  bases  are  more  or 
less  split  up  into  electrically  charged  ions  on 
dissolving  in  water. 

According  to  Faraday's  law,  hydrogen  and  the 
metallic  radicles  are  positively  charged,  while 
hydroxyl  and  radicles  are  negatively  charged. 

Acids  in  aqueous  solutions  are  supposed  to  act  as 
such  by  virtue  of  the  free  hydrogen  ions  present. 
Consequently  the  hydrogen  ions  in  a  given  equiva- 
lent of  acid  are  said  to  determine  its  strength  as 
an  acid. 

These  H  ions  are  also  supposed  to  have  the  power 
of  carrying  electricity,  and  consequently  the  more 
free  ions  present  the  greater  will  be  the  carrying 
power,  or  conductivity  of  the  solution. 

Beyond  a  certain  stage  of  aqueous  dilution 
Kohlrausch  found  that  the  molecular  conductivity 
of  these  substances  reached  a  maximum  value. 

The  dissociation  theory  implies  that  at  this  point 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  107 

the  substance  is  entirely  split  up  into  ions,  or,  in 
other  words,  completely  dissociated. 

Having  therefore  determined  the  molecular  con- 
ductivity of  an  acid  at  infinite  dilution  (that  is  to  say, 
at  the  point  of  maximum  dissociation),  its  molecular 
conductivity  at  any  other  dilution  greater  than  that 
will  vary  as  the  number  of  ions  present. 

So  that  the  ratio  of  the  molecular  conductivity  at 
any  dilution  v  to  the  molecular  conductivity  at 
infinite  dilution  will  give  the  degree  of  dissociation  at 
any  other  dilution  thus  : 


Uoo 

The  future  investigations  on  the  action  of  dyeing 
will  certainly  be  closely  connected  with  the  abnormal 
actions  of  substances  in  the  colloid  state.  When  the 
nature  of  the  fibres  and  dyes  is  considered,  it  will  be 
seen  that  every  dyer  should  have  at  least  an  elemen- 
tary knowledge  of  the  properties  and  actions  of  these 
bodies. 

The  further  study  of  this  subject  must  un- 
doubtedly lead  to  important  results.  Whether  the 
advanced  views  held  by  some  investigators  will  be 
ultimately  accepted,  or  not,  is  hardly  a  fit  subject  for 
speculation.  The  study  of  these  substances,  their 
properties,  and  their  relations  to  other  materials 
with  which  they  may  be  brought  into  contact,  is  a 
wide  one  ;  and  many  years  will  probably  elapse 
before  our  knowledge  is  brought  down  to  anything 
like  a  firm  or  satisfactory  basis. 

Be  this  as  it  may,  sufficient  facts  have  already 


io8         CHEMISTRY  AND  PHYSICS  OF  DYEING 

come  to  light  to  lead  us  greatly  to  modify  our  views 
and  theories,  and  undoubtedly  this  disturbing  influ- 
ence will  tend  to  become  greater  rather  than  to 
decrease. 

Not  the  least  important  result  of  these  investiga- 
tions will  certainly  be  directly  to  influence  our 
ideas  on  the  so-called  ionic  theory  of  solution.  It 
may  be  that  they  will  lead  to  its  destruction  or  they 
may  possibly  add  additional,  and  perhaps  it  may 
be  said,  much- wanted  confirmation  of  the  general 
principles  laid  down  by  those  who  support,  and  up- 
hold it  against  an  increasing  number  of  opposing 
facts.  At  any  rate,  the  study  of  colloids  when  in 
a  state  of  pseudo-solution  cannot  fail  to  indicate 
fresh  lines  of  research,  which  may,  in  their  general 
effect,  help  us  to  understand  many  points  which 
are  at  present  beyond  our  range  of  thought,  and 
experience. 

It  is  here  also,  that  the  true  relations  between 
dyeing  and  physical  chemistry  will  become  evident. 

There  is  little  doubt  but  that  many  actions  which 
are  of  but  everyday  interest  to  the  dyer,  and  at 
present  almost  beneath  the  consideration  of  the 
physicist,  will  be  ultimately  recognised  as  of  prime 
importance,  and  lead  to  a  general  extension  of 
knowledge. 

A  rapid  survey  of  the  actions  which  make  up  this 
most  useful  art  will  make  this  at  once  evident.  The 
extreme  delicacy  of  the  colour  reactions,  the  nature 
of  the  dyes,  the  extreme  complexity  of  the  problem, 
which  deals  with  the  ultimate  determination  of  the 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  109 

fibre-state,  and  all  that  this  entails,  indicate  that 
the  future  study  of  this  subject  cannot  but  have  its 
direct  influence  on  the  general  considerations  upon 
which  we  shall  ultimately  base  our  knowledge  and 
theoretical  speculations  on  the  state  of  matter, 
and  the  forces  which  influence  it. 

Graham  divided  all  substances  into  two 
classes,  viz.,  crystalloids  and  amorphous  substances 
(colloids).  We  already  know  that  this  division  is  of 
an  arbitrary  nature ;  but  in  the  absence  of  a  direct 
method  of  accurately  determining  the  condition  of 
the  state  taken  up  by  these  units  in  solution,  as 
regards  the  exact  condition  of  the  dissolved  sub- 
stance, we  are  unable  at  present  to  do  much  more 
than  indicate  that  this  division,  like  so  many  others 
which  were  set  up  during  the  nineteenth  century,  is 
not  altogether  a  satisfactory  one. 

Crystalloids  undoubtedly,  when  dissolved  in,  say, 
water,  change  its  physical  properties  to  a  marked 
degree.  They  diminish  the  vapour  tension,  lower  the 
freezing-point,  and  raise  the  boiling-point.  In  fact, 
they  act  as  if  there  exists  a  more  or  less  close  relation- 
ship between  the  molecules  of  the  solution  and  the 
solute,  which  modifies  the  normal  properties  of  the 
solvent  liquid. 

On  the  other  hand,  the  so-called  colloids  do  not 
seem  to  enter  into  so  close  a  relationship  with  the 
solution  system,  and  this  seems  to  be  confirmed  by 
the  fact  that  the  molecules  of  the  latter  seem  to  be 
present  in  a  state  of  higher  aggregation. 

Correspondingly,  they  exert  little  influence  on  the. 


no         CHEMISTRY  AND  PHYSICS  OF  DYEING 

state  of  the  solvent,  for  they  do  not  materially  alter 
its  freezing-  or  boiling-point  or  the  vapour  tension. 
These  bodies  are  therefore  regarded  more  in  the 
light  of  mixtures,  or  suspensions  than  true  solutions. 
But  all  these  divisions  are  of  an  arbitrary  nature, 
and  only  serve  as  stepping-stones  on  our  way  to  a 
serviceable  appreciation  of  the  true  facts  of  the  case. 
They  are  crude,  and  must  never  be  accepted  as  any- 
thing more  than  the  scaffolding,  which  will  ultimately 
be  removed  when  our  knowledge  is  more  complete. 

Although  in  some  ways  the  relationship  between 
the  solution  and  solute  seems  to  indicate  that  colloids 
do  not  enter  into  such  close  relationship  with  the 
solution,  yet  it  must  not  be  lost  sight  of  that  they 
persistently  retain  what  we  call  "  water  of  hydra- 
tion."  This,  taken  in  conjunction  with  the  above 
facts,  will  indicate  the  extreme  complexity  of  the 
reactions  which  govern  the  relative  relations  between 
the  two  systems, 

(Solution  +  crystalloid)  and  (solution  +  colloid), 
and  the  impossibility  of  our  natural  division  being 
anything    more  than    a   very  incomplete    and   un- 
satisfactory one. 

Colloids  when  mixed  with  water  will  generally 
form  jellies  when  the  proportion  of  colloid  to 
water  is  within  certain  limits.  In  certain  cases,  the 
structure  of  these  is  so  coarse  that  it  maybe  visible 
to  the  eye  under  a  low  power  objective.  It  is  then 
seen  to  consist  of  a  more  or  less  solid  framework 
through  which  the  liquid  is  dispersed. 

The  two  states  in  which  a  colloid  can  exist  in  a 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  in 

solution  state,  using  this  term  in  its  widest  sense,  are 
termed  the  hydrosol  state  and  hydrogel  state  respec- 
tively. 

In  its  outward  condition,  the  former  resembles 
a  true  solution,  such  as  a  solution  of  sugar  in  water. 
The  latter  is  of  the  nature  of  a  jelly,  and  may  be 
regarded  as  a  two-phase  state. 

The  dividing  line  between  these  two  states  is,  in  a 
way,  a  sharp  one.  It  has  been  said  that  the  critical 
point  between  them  is  as  sharp  as  the  crystallising 
point  of  an  ordinary  salt,  but  our  knowledge  of  this 
alteration  in  the  solution  state  when  the  one  passes 
into  the  other  is  very  indefinite.  It  is  difficult  to 
form  anything  like  a  mental  picture  of  what  goes  on 
during  the  transition  stage. 

This  idea  of  the  solid  framework  through  which 
the  liquid  is  dispersed  is  perhaps  the  best,  and  only 
one,  we  have  before  us,  which  may  indicate  the  fibre 
state  of  a  silk  filament  at  the  time  of  dyeing.  A 
similar  state  probably  exists  in  the  case  of  artificial 
silk  under  similar  conditions. 

In  the  case  of  other  fibres  our  ideas  of  their  con- 
struction will  be  modified  from  time  to  time,  as  our 
knowledge  of  their  physical  structure  increases. 

The  crystalloids  are  capable  of  forming  solutions 
which  are  perfect  enough  to  pass  through  the  inter- 
stices of  these  colloid  jellies  with  considerable 
freedom.  This  very  interesting  fact  must  be  care- 
fully considered  in  its  relation  to  the  presence  of 
these  bodies  in  the  dye  solution,  and  their  possible 
action  in  dyeing.  As  a  rn.atter  of  fact,  the  rate  of 


112 


CHEMISTRY  AND  PHYSICS  OF  DYEING 

diffusion  of  these  bodies  through  gelatine  or  agar- 
agar  is  practically  the  same  as  that  through  pure 
water. 

This  was  clearly  pointed  out  by  Voigtlander  (Zeit. 
/.  Phys.  Chem.y  1889,  3,  316),  who  closely  studied  this 
question.  The  influence  of  temperature  on  the  rate 
of  diffusion  is  very  marked.  An  increase  in  tem- 
perature will  greatly  increase  the  rate  at  which  the 
salt  will  equalise  itself  over  the  whole  solution  system. 

When  the  action  of  temperature  on  dyeing  is 
considered,  it  will  be  seen  that  this  action  is  one  of 
special  significance. 

The  following  table  indicates  the  relative  rate  of 
diffusion  through  agar-agar  of  some  typical  sub- 
stances at  different  temperatures. 


Substance 

at  o° 

at  20° 

at  40° 

Formic  acid    . 
Acetic  acid 

472 
.318 

.867 
.640 

1.49 
1.04 

KHO      .... 

I.OI 

i-75 

2.36 

KC1        .         . 

.786 

1.40 

2.18 

On  the  other  hand,  the  so-called  colloids  cannot 
pass  through  jellies  or  membranes  except  at  very  slow 
rates.  It  is  only  recently  that  it  has  been  recognised 
that  these  bodies  will  pass  at  all.  Dialysis,  or  the 
separation  of  colloids  from  crystalloids  in  their  solu- 
tions is  founded  on  this  fact,  and  is  a  process  in 
common  use  in  chemical  analysis. 

The  explanation  of  this  action  is  obscure.  Our 
knowledge  of  the  subject  is  limited,  and  the  possi- 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  113 

bility  of  colloids  passing  through  membranes  is  one 
which  deserves  further  attention. 

Just  as  it  is  possible  to  prepare  membranes  which 
are  permeable  to  water,  but  which  will  stop  the 
passage  of  some  salts  (crystalloids),  so  at  least  some 
colloids  are  capable  of  slowly  passing  through  certain 
membranes. 

These  semi-permeable  membranes,  which  will  stop 
the  passage  of  crystalloids  in  some  cases,  are  natur- 
ally closer  in  their  structure  than  the  ordinary  ones. 
A  porous  pot  holding  in  its  structure  a  gelatinous 
precipitate  of  ferrocyanide  of  copper  will  act  in  this 
way.  (Proc.  Chem.  Soc.y  lix.  344.) 

It  is  interesting  as  a  matter  of  history  to  note  that 
this  passage  of  liquids  through  films  (parchment 
paper,  bladders,  &c.,)  which  is  called  osmosis,  was 
first  noticed  by  Abbe  Nollet  in  1748. 

It  may  be  here  mentioned,  and  it  is  pointed  out 
in  fuller  detail  elsewhere,  that  in  considering  the 
cause  of  this  action  which  leads  to  diffusion  it  is  not 
sufficient  to  assume  that  the  size  of  the  aggregates 
in  solution  is  the  only  controlling  factor. 

The  author  has  attempted  to  explain  the  slow 
dialysis  of  colloids  by  assuming  that  molecular  migra- 
tion takes  place  in  pseudo  solutions  from  one  aggre- 
gate to  the  other. 

This  idea  of  molecular  migration  in  pseudo  solu- 
tions is  founded  by  analogy,  on  the  Poisson  theory  of 
atomic  migration.  It  offers  a  possible  explanation 
of  the  mechanism  of  the  dialysis  of  colloids  (Dreaper, 
/. S.C.I.,  xxiv.  223,  and  J.S.D.  and  C.y  May  1905). 

8 


H4         CHEMISTRY  AND  PHYSICS  OF  DYEING 

This  migration  of  the  individual  molecules  from 
one  complex  to  another  may  explain  the  slow  dyeing 
action,  or  absorption  of  lakes  like  those  of  alizarine 
by  the  one-bath  method,  where  the  so-called  mole- 
cular weight  of  the  aggregates  is  a  high  one ;  the 
"levelling  up''  action  in  dyeing;  the  passing  of  a 
solution  of  gun-cotton  through  a  membrane ;  and  the 
slow  "ripening"  of  solutions  of  cellulose,  or  its  com- 
pounds, in  the  manufacture  of  artificial  silk. 

By  assuming  this  action,  it  is  possible  to  explain 
the  slow  passage  of  large  aggregates  through  a 
membrane,  or  "sieve,"  where  the  direct  passage 
is  prohibited  by  size. 

An  alternative  explanation  given  by  Prof.  Ramsay 
(/.5.C.J.,  1904,  296)  is,  that  the  cotton  molecules 
may  become  deformed  in  shape,  and  glide  through 
the  interstices  of  the  membrane  like  worms. 

If  a  solution  of  a  crystalloid  be  separated  by  a 
porous  membrane  from  pure  water,  certain  so-called 
osmotic  phenomena  are  set  up,  and  enormous  pres- 
sures may  result  from  this  action. 

This  osmotic  pressure  may  be  measured  directly, 
or,  more  easily  calculated.  In  the  case  of  mineral 
acids  and  salts  the  actual  pressure  is  in  excess  of  the 
calculated  results.  From  certain  theoretical  conclu- 
sions Arrhenius  accounts  for  this  by  assuming  the 
dissociation  of  the  acid,  or  salt.  In  this  way  the 
number  of  individual  units  in  solution  is  increased, 
and  with  it  the  pressure,  or  osmotic  effect. 

There  is  no  generally  accepted  view  as  to  the 
cause  of  osmotic  pressure. 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  115 

The  dissociation  theory  assumes  that  the  dis- 
solved substance  exists  in  the  solution  in  a  state,  so 
far  equivalent  to  a  perfect  gas,  that  it  obeys  laws, 
which  are  similar  to  those  governing  the  latter. 

The  association  theory,  on  the  other  hand, 
assumes  some  attractive  force  at,  work  which  forms 
aggregates  consisting  of  solvent  and  solute  mole- 
cules. At  any  rate,  the  phenomena  of  osmosis  are 
directly  connected  with  the  state  of  the  solution  at 
the  time  they  are  exhibited,  varying  with  the  con- 
dition of  the  solute,  and  its  solution  state.  Action 
at  the  surfaces  of  the  membrane  also  seems  to  play 
an  important  part  in  these  phenomena. 

The  absorption  of  water  by  colloids  is  clearly  of 
the  first  importance  to  the  dyer.  The  preliminary 
operations  to  dyeing,  apart  from  the  question  of  the 
colour  and  gloss  of  the  fibre,  and  its  condition  during 
the  mechanical  stages  of  its  manufacture,  are  chiefly 
connected  with  the  object  of  presenting  the  fibre  in 
a  uniform  condition  to  the  dye-bath.  All  foreign 
substances  of  a  nature  which  will  defeat  this  end, 
such  as  wax,  grease,  &c.,  are  as  far  as  possible 
removed  by  alkaline,  or  other  treatment.  The 
thorough  wetting  out  of  the  fibre  before  it  is  brought 
into  the  presence  of  mordant,  or  dye,  is  also  well 
understood,  and  its  need  cannot  be  over-estimated. 

From  the  theoretical  point  of  view,  all  these 
operations  are  conducted  with  the  object  of  equally 
permeating  the  fibre  substance  with  the  aqueous 
solutions.  The  result  of  this  is  to  obtain  a  fibre 
condition,  corresponding  more,  or  less,  to  the  so-called 


n6         CHEMISTRY  AND   PHYSICS  OF  DYEING 

hydrogel  state  and  as  far  as  possible  an  equal  state 
of  hydration. 

A  study  of  the  way  in  which  silicic  acid  gives  up 
its  water  of  hydration  indicates  the  state  in  which  it 
is  held.  The  elimination  of  water  by  this  hydrogel 
is  a  gradual  and  continuous  one,  decreasing  as  the 
anhydrous  state  is  reached  (Bemmelen,  Zeit.  Anorg. 
Chem.y  13,  233). 

The  influence  of  these  hydrogels  on  the  properties 
of  the  tl  solvent  "  is  small. 

The  colloids  exert  little  or  no  influence  on  osmotic 
pressure,  boiling-point,  freezing-point,  or  electrical 
conductivity  of  the  solution,  and  in  this  way  differ 
entirely  from  crystalloids. 

It  has  been  shown  that  solutions  of  these  colloids 
may  be  made  to  gelatinise,  or  enter  the  hydrogel  state, 
by  the  addition  of  small  quantities  of  certain  sub- 
stances. This  action  is  different  to  that  shown  when 
a  crystalloid  is  made  to  partly  leave  the  soluble  state 
in  a  supersaturated  solution,  by  the  addition  of  a 
crystal,  or  other  substance.  It  is  only  local  in  its 
effect  in  the  case  of  colloids. 

The  hydrogels  have  undoubtedly  the  power  of 
absorbing  foreign  substances  in  solution.  For  in- 
stance, metastannic  acid  readily  absorbs  hydrochloric 
acid,  or  sodium  sulphate,  and,  probably,  many  other 
substances  (Bemmelen  and  Klobbie,  Zeit.  Anorg. 
Chem.,  23,  in).  The  concentration  of  the  hydro- 
chloric acid  was  often  found  to  be  greater  than  in  the 
solution.  The  absorption  factor 

K  =  cone,  in  colloid  /  cone.  in]H,O, 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  117 

is  not  a  constant  in  this  case,  but  is  dependent  on  the 
concentration  at  the  point  of  equilibrium. 

A  further  point  is  that  the  absorption  of  sub- 
stances is  proportional  to  the  hydration  of  the  colloid. 
This  is  of  the  greatest  interest  from  the  dyer's  point 
of  view.  It  is  found  that  silicic  acid  absorbs  com- 
pounds in  the  ratio  of  its  state  of  hydration  (Bem- 
melen,  /.  fur  Chem.,  23,  324).  Similar  interesting 
results  were  also  obtained  with  SnO2  in  different 
states  of  hydration. 

SnO2.2-3H2O  absorbed  more  acid  than  SnO2.i.2  H2O. 

When  we  consider  the  conditions  of  the  fibres 
which  give  the  best  dyeing  results,  so  far  as  dye 
absorption  is  concerned,  it  will  at  once  be  seen  how 
closely  they  approximate  to  those  which  give  the 
highest  absorption  results  in  the  cases  of  inorganic 
hydrogels  given  above. 

The  importance  also  of  an  equal  state  of  hydration 
from  the  dyeing  point  of  view  is  clear  when  we 
remember  that  it  is  very  desirable  to  obtain  an  even 
shade,  or  absorption  of  dye.  This  is  a  necessary 
condition  so  far  as  piece  or  yarn  dyeing  is  concerned, 
in  practically  all  cases,  although  not  so  necessary 
in  dyeing  loose  wool,  or  cotton. 

So  that  the  condition  of  the  fibre  at  the  time  of 
dyeing  is  of  the  first  importance,  and  probably  the 
conditions  of  the  dye  solution  are  unconsciously 
arranged  or  determined  by  the  dyer  as  much  with 
the  object  of  obtaining  a  correct  fibre  condition,  as 
modifying  the  physical  (or  chemical)  state  of  the  dye 


n8         CHEMISTRY  AND  PHYSICS  OF  DYEING 

solution.  The  dyer  must  recognise  the  possible  and 
variable  action  of  the  fibre  as  well  as  the  dye-stuff, 
when  the  conditions  of  dyeing  are  altered. 

Hydrogels,  particularly  those  of  the  dioxides  of 
silicon,  tin,  magnesium,  &c.,  can  form  absorption 
compounds  with  gases  and  liquids,  and  are  able  by 
absorption  to  remove  acids,  bases,  salts,  &c.,  from 
solutions  in  which  they  are  placed. 

This  action  goes  on  until  a  state  of  equilibrium  is 
established.  The  state  of  equilibrium  alters  under 
changed  conditions  of  temperature,  strength  of  solu- 
tion and  amount  of  liquid  per  unit  of  hydrogel. 

The  principal  phenomena  of  absorption  have  been 
described  as  follows  (Bemmelen,  Landw.  Versuchs. 
Stat.,  35,  69) : 

(1)  When  an  absorbent  substance  gains,  or  loses 
some  of  the  absorbed  substance,  in  all  probability 
each  particle  becomes  equally  richer,  or  poorer,  in  the 
absorbed  substance.     In  this  way  they  differ  from 
chemical  compounds.     When  the  latter  suffer  dis- 
sociation a  certain  number  of  molecules  are  com- 
pletely decomposed,  and  the  rest  remain  intact. 

(2)  The  power  of  absorption  is  not  constant,  but 
varies  as  the  action  goes  on.     The  attraction  for  the 
first    portion  is  strong.     As  more  is  absorbed    the 
tendency  to  absorb  decreases  rapidly.     The  action 
takes  place  more  slowly.     In  the  same  way  the  latter 
portion  is  given  up  more  readily  to  solutions. 

(3)  The  absorptive  power  of  colloids  varies  with 
their   method   of   production,    and   the   subsequent 
treatment  they  are  exposed  to. 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  119 

(4)  Hydrogels  may  change  into  ordinary  chemical 
hydrates  acquiring  a  definite  composition,  and  even 
a  crystalline  form.     In  doing  so  they  lose  the  power 
of  forming  absorption   compounds. 

It  would  seem,  therefore,  that  at,  say,  a  higher 
temperature  the  residual  chemical  attraction  is  more 
definitely  confined  to  the  hydrate  complex. 

This  is  indicated  also  in  the  fact  that  the  forma- 
tion of  a  colloid  compound  is  accompanied  by  the 
evolution  of  considerably  less  heat  than  is  evolved 
in  the  formation  of  the  corresponding  crystalline 
form. 

(5)  Increase  of  temperature  affects  the  absorptive 
power.     It  sets  free  a  certain  amount  of  water  from 
the  hydrogel,  and  also  increases  the  solvent  action  of 
the  water,  or  the  substance  absorbed. 

Consequently  the  rate  of  absorption  decreases. 

(6)  Every  hydrogel  has  its  own  specific  rate  of 
absorption  for  each  acid,  base,  or  salt.     One  hydrogel 
may  absorb  acids  more  powerfully  than  it  does  other 
substances,    another    one    will    absorb    bases    more 
powerfully,  and  another  salts.     In  general,  absorp- 
tion is  strongest  when  under  the  circumstances  the 
hydrogel,  and  the  absorbed  compound  can  combine 
chemically.     An   example    of    this    action  is   seen 
in  the   case  of  stannic  acid.     This  absorbs  a  good 
deal    of    sulphuric    acid,   but    much    more    potash. 
(a)  The  substance  dissolved  may  be  proportionately 
divided  between  the  water  of  the  hydrogel  and  the 
water  of  the  solution,  as  in  the  case  where  potassium 
chloride    is    absorbed    by    the    hydrogel    of    silica. 


120          CHEMISTRY  AND  PHYSICS  OF  DYEING 

(&)  The  hydrogel  may  absorb  a  larger  proportion 
of  the  dissolved  substance.  The  hydrogel  of  meta- 
stannic  acid  will  absorb  nearly  all  the  potash  from  a 
solution. 

This  absorption  may  even  cause  decomposition 
of  the  dissolved  substance.  The  hydrogel  of  silica 
will  remove  potash  from  potassium  carbonate,  or  soda 
from  disodium  phosphate.  On  shaking  up  the  same 
hydrogel  with  calcium  carbonate  and  potassium  chlo- 
ride, there  is  an  absorption  of  lime  and  potash,  and  a 
corresponding  amount  of  calcium  chloride  and  calcium 
bicarbonate  remains  in  solution.  Some  potassium 
chloride  is  also  absorbed. 

(7)  The  condition  of  the  hydrogel  and  its  weight 
being  given,  the  temperature  also  being  known 
and  remaining  constant,  and  the  hydrogel  not  being 
soluble  in  the  solution,  the  amount  of  a  particular 
substance  absorbed  by  it  varies  with  the  state  of 
concentration,  and  with  the  amount  of  solution. 

A  state  of  equilibrium  is  established  between  the 
absorptive  action  of  the  hydrogel  on  the  one  hand, 
and  the  opposing  action  of  the  water  on  the  other. 
If  chemical  decomposition  also  takes  place,  the 
attraction  of  chemical  combination  takes  part  in 
producing  the  equilibrium. 

The  stronger  the  solution  the  more  of  the  sub- 
stance is  absorbed,  but  in  decreasing  quantity.  The 
limit  is  reached  when  after  the  equilibrium  is  estab- 
lished the  liquid  is  in  a  saturated  condition.  No 
satisfactory  formula  can  be  obtained  to  represent 
the  action  generally,  except  in  very  dilute  solutions, 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  121 

and  where  the  absorptive  power  of  the  colloid  is  weak, 
when  the  curve  obtained  is  practically  a  straight  line. 

(8)  One  crystalloid  absorbed  by  a  hydrogel  may 
be  replaced  by  another. 

If  a  hydrogel  which  has  absorbed  A  be  placed  in  a 
solution  of  a  substance  B,  then  the  solvent  will  dis- 
solve out  some  of  A,  and  at  the  same  time  some  of  B 
will  be  absorbed  until  equilibrium  is  established,  but 
no  true  substitution  takes  place. 

If  the  absorption  quantities  are  small,  A  and  B 
are  absorbed  without  mutually  influencing  one  other 
to  a  noticeable  extent.  If  the  quantities  of  A  be 
large,  there  may  be  a  loss  by  substitution. 

The  last  part  of  A  absorbed,  which  is  not  held 
so  strongly,  may  be  replaced  by  B. 

It  has  been  noticed,  however,  that  by  repeatedly 
treating  the  hydrogel  with  solutions  of  B,  the 
latter  may  entirely  replace  A.  In  the  event  of 
chemical  action  taking  place  between  A  and  B  in 
solution,  the  action  maybe  greatly  complicated,  and 
even  entirely  altered. 

The  ultimate  absorption  of  the  substance  by  the 
hydrogel  depends  entirely  upon  the  final  state  of  the 
solution. 

An  important  statement  has  been  made  by 
J.  Billitzer  (Zeit.  Phys.  Chem.,  1903,  45,  307),  as  a 
result  of  some  experiments  on  the  "  carrying  down  " 
of  calcium,  chromium,  sodium  and  potassium  chlo- 
rides when  they  precipitate  colloids.  The  fact  seems 
to  be  established  that  they  act  in  the  ratio  of  their 
chemical  equivalents  in  their  precipitating  action. 


122          CHEMISTRY  AND  PHYSICS  OF  DYEING 

If  potassium  chloride  is  used  as  the  precipitating 
electrolyte,  acid  is  set  free  when  the  colloid  is  electro- 
negative ;  on  the  other  hand,  when  the  colloid  sub- 
stance is  electropositive  alkali  is  liberated. 

The  colloids  may  be  divided  into  two  classes, 
according  to  their  action,  when  under  the  influence 
of  a  high  E.M.F.,  and  may  be  classified  into  electro- 
positive and  electro-negative  units,  as  the  case 
may  be. 

The  electro-negatively  charged  particles  move  to 
the  anode,  and  the  electro-positive  ones  to  the  cathode. 

Colloids,  or  suspensions,  which  are  charged  in 
opposite  directions  will  precipitate  each  other  if 
present  in  certain  proportions. 

Aniline  dyes  act  as  colloids  in  this  respect.  The 
acid  dyes  were  found  to  migrate  towards  the  anode 
and  the  basic  dyes  towards  the  cathode  (Neisser 
and  Friedemann,  Chem.  Centr,  1904,  i,  1387). 

The  coagulating  effect  produced  on  solutions  of 
colloids  by  reagents  is  of  a  complicated  nature.  It 
does  not  seem  possible  to  give  any  definite  reason  for 
their  action.  We  must  content  ourselves  with  the 
recorded  facts  which  in  themselves  seem  very  con- 
tradictory ;  they  at  least  indicate  the  very  complex 
nature  of  the  phenomena  before  us. 

The  one  thing  which  seems  certain  is  that  electro- 
lytes, or  soluble  salts,  have  the  power  of  degrading 
hydrosols  into  hydrogels,  and  that  in  doing  so  the 
precipitating  reagent  may  be  partly,  or  wholly, 
precipitated  at  the  same  time.  It  must,  however, 
be  remembered  that  other  substances  will  also  preci- 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS   123 

pitate  colloids.  That  this  action  may  be  of  a 
mechanical  nature  is  seen  in  the  fact  that  if  barium 
sulphate  is  shaken  up  with  some  hydrosols,  it  will 
carry  down  with  it  a  good  deal  of  the  colloid 
substance. 

In  other  cases,  we  may  have  a  soluble  salt 
acting  in  this  way,  and  being  decomposed  in  the 
process. 

J.  Duclaux  (Compt.  rend.,  1904,  138,  571)  affirms 
that  the  precipitated  colloid  usually  contains  a 
certain  amount  of  one  of  the  radicles  of  the  salt  used 
to  produce  coagulation,  the  change  being  produced 
by  simple  substitution  of  one  of  its  radicles  for  an 
equivalent  amount  of  one  of  the  constituents  of  the 
colloidal  substance.  The  solution  after  coagulation 
will  contain  a  small  amount  of  the  radicle  displaced 
from  the  colloid.  Linder  and  Picton's  recent  work 
seems  to  support  this. 

It  seems  that  in  the  neighbourhood  of  the  coagu- 
lating point  a  slight  change  in  equilibrium  will  pro- 
duce a  much  larger  visible  effect  on  the  colloid, 
so  that  the  latter  is  easily  precipitated. 

The  precipitation  of  proteid  substances  by  acids, 
copper,  or  silver  salts  is  in  each  case  a  reversible  one, 
the  precipitate  dissolving  in  excess  of  the  reagent. 
(V.  Henri  and  A.  Meyer,  Compt.  Rend.,  1904,  138, 
757.)  This  is  a  reaction  which  it  will  be  advisable  to 
keep  before  us  in  the  study  of  the  action  of  mordants 
and  dyes.  It  may  be  possible  to  explain  certain 
reactions  in  this  way,  which  at  present  are  more  or 
less  obscure. 


124          CHEMISTRY  AND  PHYSICS  OF  DYEING 

It  would  follow  that  the  composition  of  the  fibre 
might  be  expected  to  have  a  great  influence  on  the 
results  produced  in  different  cases. 

All  inorganic  colloids  seem  to  be  more  or  less 
absorbed  by  cotton,  wool,  or  silk  fibres.  This  is 
stated  to  be  quite  independent  of  the  chemical 
nature  of  the  dissolved  colloid.  (W.  Biltz,  Ber.y 

I9°4,  37,  1766-) 

It  is,  perhaps,  not  safe  to  argue  from  the 
inorganic  to  the  organic  colloids  so  far  as  their 
general  reactions  are  concerned,  for  the  inorganic 
colloids  seem,  at  best,  to  be  present  in  a  very  degraded 
state  in  their  solutions.  As  has  before  been  pointed 
out,  they  may  be  carried  down  in  a  mechanical  way 
by  such  rough  suspensions  as  barium  carbonate,  and 
are  then  firmly  held  against  resolution.  Organic 
colloids  such  as  dyes  are  not  so  readily  carried  down, 
or  held,  in  this  way. 

In  passing  it  is  interesting  to  note  that  the  method 
of  precipitation  of  insoluble  salts  in  colloids  like 
gelatine,  is  of  an  irregular  nature,  so  far  as  distribu- 
tion is  concerned.  Liesegang  noticed,  for  instance, 
that  silver  chromate  precipitated  in  situ  (in  capillary 
tubes)  by  the  diffusion  of  silver  nitrate  solution 
into  gelatine  in  which  potassium  chromate  has  been 
dissolved,  gives  rise  to  unequal  precipitation.  The 
silver  chromate  occurs  in  laminae  at  right  angles  to 
the  direction  of  the  tube. 

The  relative  condition-state  of  hydrosols  and 
hydrogels  so  far  as  is  known,  is  as  follows.  The  two 
states  seem  to  be  in  a  way,  distinct,  that  is  to  say, 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS    125 

there  is  generally  a  critical  point  in  the  passage  from 
one  state  to  the  other  which  corresponds,  in  a  rough 
way,  with  the  difference  between  the  solid  and  liquid 
state  in  ordinary  substances.  This  statement  must 
only  be  taken  in  a  general  sense.  Further  knowledge 
may  indicate  that  the  dividing  line  is  an  imaginary 
one,  but  for  practical  purposes  we  may  consider  the 
two  states  as  distinct.  Taking  the  hydrogel  state  as 
consisting  of  a  framework,  more  or  less  perfectly 
developed,  as  the  case  may  be,  permeated  by  a  liquid, 
it  may  be  said  to  be  a  two-phase  system— the  frame- 
work or  more  insoluble  portion  corresponding  with 
the  solid  phase,  and  the  other  with  the  solution  state. 
In  this  gelatinised  state  the  water  may  be  partly  held 
by  capillary  action.  The  power  with  which  colloids 
will  take  up  moisture  is  immense.  The  molecular 
forces  which  come  into  play  when  colloids  lose 
water  are  correspondingly  great.  Gelatine  on  drying 
will  strip  off  the  surface  of  a  containing  glass  vessel. 

The  rate  at  which  chemical  action  may  take  place 
in  colloid  solutions  is  not  altered  to  any  great 
extent. 

The  classification  of  the  colloids  is  evidently 
impossible  at  present.  It  has  been  proposed  to 
divide  them  roughly  into  two  classes,  having  res- 
pectively a  molecular  weight  either  above  or  below 
20,000.  In  the  former  we  find  starch  (25,000),  silicic 
acid  (49,000),  and  in  the  latter  would  come  tannin, 
dextrin,  ferric  hydroxide  (6000). 

It  would  seem  that  it  is  the  colloids  of  higher 
molecular  weight  which  give  non-reversible  solutions 


126         CHEMISTRY  AND  PHYSICS  OF  DYEING 

on  freezing.     (Linnebarger,  /.  Am.  Chem.  Soc.  20, 

1898, 375.) 

Such  proposed  methods  of  separation  as  that  of 
shaking  up  the  solution  with  barium  sulphate  hardly 
deserve  attention. 

Until  we  more  thoroughly  realise  the  state  in 
which  colloids  exist  in  pseudo  solutions,  it  will  be 
impossible  to  derive  any  satisfactory  method  of 
classification. 

There  is  need  for  a  standard  of  solution,  and 
a  ready  method  of  comparison  with  other  states. 
This  may  either  take  the  form  of  a  standard  solu- 
tion, or  a  calibrated  porous  partition  for  diffusion 
experiments. 

A  colloid  which  seems  dry  to  the  touch  (such  as 
gelatine  or  silk)  contains  a  considerable  amount  of 
water,  which  it  may  lose  on  further  drying  at  a 
temperature  of  100°  C.,  the  state  of  the  fibre  continu- 
ally changing  with  its  composition.  This  action,  at 
ordinary  temperature,  may  be  a  reversible  one.  If  a 
colloid  be  dried  so  that  its  vapour  tension  is  nil, 
it  may  regain  its  water  partially,  or  entirely,  on 
exposure  to  the  air.  This  will  depend  on  the  com- 
plete reversibility  of  the  process,  and  will  vary  with 
different  substances  and  conditions. 

In  a  closed  space  partially  saturated  with  mois- 
ture, a  colloid  loses  water  until  its  vapour  tension 
is  equal  to  that  of  the  surrounding  medium. 

The  rapidity  of  dehydration  constantly  diminishes 
until  it  reaches  a  minimum  as  the  vapour  tension 
approaches  that  of  the  enclosed  air.  For  example, 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS   127 

colloidal  metastannic  acid  containing  2.2  mols.  of 
water  lost  .55  mols.  the  first  day.  The  quantity 
lost  decreased  gradually,  until  on  the  I3th  day  only 
.01  mol.  per  day  was  lost,  and  the  composition  was 
.79  mol.  OH2.  (Bemmelen,  Rec.  Trav.  Chim.,  7,  37.) 

When  this  process  of  "  hydration  "  becomes  non- 
reversible,  which  happens  when  most  colloids  lose 
water,  especially  when  drying  at  a  high  temperature 
complicates  the  action/the  non-reversible  modifications 
have  a  diminished  absorptive  power,  but  at  the  same 
time  they  retain  their  water  with  more  energy.  This 
is  an  indication  that  the  secondary  chemical  action 
involved  may  be  constant  in  its  amount,  varying  in 
intensity  with  the  ratio  of  colloid  to  water.  In  the 
transformation  of  a  colloid  into  a  true  hydrate  a  state 
of  equilibrium  is  reached  with  fewer  molecules  of 
water,  with  the  formation  of  correspondingly  larger 
aggregates.  It  may  undergo  modification  at  a 
suitable  temperature,  so  that  it  becomes  insoluble 
in  the  medium  in  which  it  was  originally  dissolved. 

Colloidal  silica  will  hold  more  water  at  50°,  or 
even  at  100°,  in  a  medium  saturated  with  aqueous 
vapour,  than  at  15°  in  dry  air.  (Ibid.  Rec.  Trav. 
Chim.y  7,  69.) 

The  precipitating  action  of  salts  on  colloids  seems 
to  be  a  general  one. 

The  idea  has  been  put  forward  that  the  precipita- 
ting action  of  colloids  is  a  dehydrating  one.  Tomasso, 
(Compt.  Rendus,  99,  37)  does  not  agree  with  this,  some 
salts,  it  being  held,  acting  in  the  opposite  direction. 
Sodium  acetate,  sodium  sulphate,  potassium  bromide,, 


128         CHEMISTRY  AND  PHYSICS  OF  DYEING 

and  potassium  chlorate  are  said  to  act  by  retarding 
the  dehydration  of  cupric  hydroxide  into  copper 
oxide.  On  the  other  hand,  potassium  chloride  and 
sodium  carbonate  act  in  the  reverse  direction. 

All  proteids  (except  peptone)  are  precipitated  by  a 
neutral  solution  of  ammonium  sulphate.  All  colloids 
seem  to  act  in  this  way,  including  soap,  soluble  carbo- 
hydrates, glycogen,  &c.  (Nasso,  Pfliiger's  Archiv. 

41,  5040 

This  writer  will  not  allow,  however,  that  the 
cause  of  the  precipitation  is  due  to  the  struggle  for 
water  which  takes  place  between  the  colloid  and  the 
salt.  A  series  of  experiments  tend  to  show  that  this 
is  not  sufficient  to  explain  the  results  obtained. 

The  presence  of  a  salt  is  not  necessary  to  preci- 
pitate the  colloids.  Plaff,  Geiger,  and  Pay  en  have 
shown  that  separation  may  take  place  by  freezing 
in  some  cases.  A  colloidal  solution  of  antimony 
trisulphide  (Schultz's  method)  is  entirely  separated 
by  freezing.  On  the  other  hand,  albumen  is  not 
separated,  or,  if  it  is,  the  action  is  a  reversible  one. 
(Lubavin,  /.  Russ.  Chem.  Soc.,.  21,  397.) 

The  reduction  of  the  freezing-point  of  water  by 
colloids  is  very  slight.  This  indicates  very  high 
figures  for  the  molecular  weights. 

Gallic  and  tannic  acids  are  said  by  Paterno  (Zeit. 
Phys.  Chem.  4,  457)  to  show  a  very  high  molecular 
weight.  When  dissolved  in  acetic  acid  they  are  said 
to  give  normal  results.  This  is,  however,  denied  by 
Sabaneeff  (/.  Rus.  Chem.  Soc.,  22,  102). 

The  state  of    egg  albumen  (15  per  cent,  sol.)  is 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS   129 

said  by  this  investigator  to  correspond  with  a  mole- 
cular weight  of  15,000. 

On  the  other  hand,  Gladstone  and  Hibbert  (Phil. 
Mag.,  26,  38)  obtained  results  by  Raoult's  method, 
which  indicate  a  molecular  weight  of  2000. 

Guthrie's  original  statement  that  colloids  do  not 
influence  the  boiling-point  (or  freezing-point)  of 
water,  or  in  other  words,  that  the  tension  of  aqueous 
vapour  of  solutions  of  colloids  equals  that  of  water, 
is  not  correct.  Gelatine,  for  instance,  is  said  to  raise 
the  boiling-point. 

The  student  is  referred  to  the  work  done  by 
Morris  (Trans.  Chem.  Soc.  1888,  610,  and  1889,  466), 
which  indirectly  is  of  interest  to  those  engaged  in 
the  study  of  the  absorption  of  dyes. 

Hydrolysis  in  solution  certainly  seems  to  take 
place  in  many  cases.  For  example,  potassium 
cyanide  is  partially  decomposed  into  KHO  and  HCN 
in  aqueous  solution  (Shields,  Phil.  Mag.,  (5)  35,  365). 
The  action  of  water  in  producing  this  effect  is  called 
hydrolysis. 

Probably  all  salts  are  hydrolysed  in  aqueous 
solution,  but  in  many  cases  to  an  exceedingly 
small  extent. 

Esters  as  well  as  salts  are  hydrolysed.  Methyl 
and  ethyl  acetates  are  decomposed  into  acetic  acid 
and  the  corresponding  alcohol.  The  extent  to  which 
hydrolysis  takes  place  is  regulated  by  mass  action. 

Veley  (/.C.S.,  1905,  26)  considers  that  the  de- 
composition of  ammonium  salts  on  boiling  is  due  to 
hydrolysis,  and  not  dissociation. 

9 


130          CHEMISTRY  AND  PHYSICS  OF  DYEING 

The  cases  where  hydrolysis  is  possible  are  said 
to  be  : 

(1)  Salts  from  weak  bases  and  strong  acids. 

(2)  Salts  from  strong  base  and  weak  acid. 

(3)  Salts  from  weak  base  and  weak  acid. 

It  would  therefore  seem  to  be  a  function  of  an 
unequal  atomic  bond,  and  this  confirms  the  above 
theory  of  association  rather  than  dissociation,  when 
the  actual  reaction  between  the  water  molecules  and 
the  solute  is  considered.  For  instance, 

KCN  +  H20  ^  HCN  +  KHO. 

The  laws  for  electrical  conductivity  in  the  above 
cases  are  stated  to  be 

,  ,     C  (acid)   x  C  (base)       v 
~C~(salt)~ 

and  in  the  case  of  (3) 

C  (acid)   x  C  (base)       K 
C2  (salt) 

In  (i)  the  amount  of  the  action  is  stated  to  depend 
on  dilution.  In  (2)  it  is  independent  of  dilution 
beyond  a  certain  limiting  value.  In  (3)  hydrolysis 
is  nil,  or  inappreciable.* 

The  influence  of  the  dissociation  of  dyes  in 
solution  has  been  discussed  by  Vignon  (Bull.  Soc. 
Ind.  de  Mulh.  1893,  407  and  J.S.D.  and  C.  1893,  44). 

*  For  further  information  on  this  subject  the  following  may  be 
consulted — Walker:  Zeit.  Phys.  Chem.,  1889,  4,  319;  Arrhenius 
(ibid.)  1894,  13,  407,  and  Van't  Hoff,  Chemische  Dynamik, 
(1898)  121-126. 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  131 

From  this  point  of  view  the  three  factors  influ- 
encing the  action  of  dyeing  would  be : 

(1)  The  absorbent  fibre  ; 

(2)  The  dye-stuff ; 

(3)  The  solvent ; 

an  equilibrium  being  established  and  determined 
by  chemical  forces,  and  the  conditions  of  dissocia- 
tion, resulting  in  any  case  in  the  dye  effect 
observed. 

This  matter  has  been  further  studied  in  greater 
detail  by  Knecht  (J.S.D.  and  C.  1898,  59  ;  1903, 158  ; 

r9°4,  59); 

Diamine  sky  blue,  for  instance,  is  said  to  dis- 
sociate quite  as  readily  as  any  basic  dye,  when  tested 
by  the  filter-paper  method. 

On  the  other  hand,  the  sulphonated  basic  dyes  like 
acid  green,  or  acid  violet,  show  no  dissociation  by  the 
above  test.  These  results  are  said  to  correspond  very 
closely  with  the  dyeing  effects  of  these  dyes  on  wool. 
The  alcoholic  solutions  of  these  dyes  do  not  show 
dissociation  by  this  test.  They  have  also  no  dyeing 
power  on  wool.  It  will  be  noticed,  however,  that 
the  possible  difference  in  the  action  of  alcohol  and 
water  on  the  fibres  themselves  is  disregarded. 

The  halo  formed  on  paper  by  this  method  with 
magenta  can  be  prevented  if  hydrochloric  acid  is 
present  in  the  free  state.  Correspondingly,  wool  will 
not  dye  in  the  same  acid  solution  of  the  dye,  and 
this  reagent  may  act  by  preventing  the  dissociation 
effect  in  both  cases. 

Acid    colours  will  show  this  separation  of  the 


132          CHEMISTRY  AND  PHYSICS  OF  DYEING 

colour  acid  (on  acidifying  the  dye  solution),  but 
as  a  general  rule  they  will  give  no  halo  in  neutral 
solutions. 

The  colour  acids  are  insoluble  when  compared 
with  their  sodium  salts.  They  are,  therefore,  prob- 
ably in  a  state  of  high  aggregation,  and  in  this  mole- 
cular condition  would  be  more  under  the  influence 
of  surface  action.  This  must  not  be  overlooked. 

It  will  be  noticed  that  the  influence  of  the  solution 
state  on  the  rate  of  dyeing  may  be  a  very  important 
factor.  Dyes  may  be  attracted  by  the  fibres  from 
some  solutions,  and  not  from  others.  They  may 
also  be  removed  from  the  fibre  in  some  cases  by  the 
second  solvent,  in  which  they  are  more  soluble. 

That  the  presence  of  moisture  is  necessary  in 
order  that  the  action  may  be  complete  seems  to  be 
confirmed  by  the  recorded  fact  that  better  results 
are  obtained  by  the  use  of  very  moist  steam  in  fixing 
direct  cotton  dyes  on  cotton  after  printing.  (Wilhelm, 
Proc.  Soc.  Ind.  de  Mulh.  1904.)  The  dyes  would  seem 
to  require  a  certain  amount  of  steam  (moisture) 
to  fix  them  under  these  conditions. 

The  exact  cause  of  this  action  is  unknown.  The 
increased  hydration  of  the  fibre  may  play  some  part 
in  the  reaction. 

Some  experiments  on  the  absorption  of  rhodamine 
base  from  solution  in  benzene  are  also  of  interest 
(Weber,  Farb.  Zeit.  1899,  i).  They  indicate  that  a 
highly  hydrated  fibre  state  is  not  necessary  for  the 
"  dyeing  "  to  take  place  in  this  case.  Cotton  fibre 
will  absorb  the  base  from  this  solution,  but  the 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS  133 

resulting  shade  is  not  very  fast  against  washing, 
indicating  that  it  is  imperfectly  fixed  in  the  fibre 
substance. 

In  the  same  way,  precipitated  cellulose,  which  is 
in  a  more  highly  hydrated  form,  will  dye  more  readily 
than  the  original  cotton  with  some  dyes.  They  are 
also  faster  against  washing.  It  must  be  remembered 
in  connection  with  this  subject  that  mercerised 
cotton  will  give  a  darker  shade  with  the  same  per- 
centage of  dye. 

It  may  be  argued  that  the  increased  absorp- 
tion is  due  to  the  greater  number  of  OH  groups 
present  in  the  cellulose  molecule,  or  aggregate.  In 
connection  with  this  it  may  be  noted  that  the 
cellulose  tetracetate,  which  is  very  resistant  to  any 
ordinary  hydrating  action  of  water,  as  tested  by  its 
physical  properties,  will  not  take  up  dyes  under 
these  conditions. 

It  has  been  stated  that  alizarine  lakes,  which  are 
soluble  in  alcohol-ether,  are  readily  dyed  on  cotton 
from  such  a  solution.  If  this  is  so,  the  matter  is  one 
of  interest,  on  which  the  writer  hopes  to  give 
further  details  later.  It  is  difficult  to  see  how 
dyeing  can  be  due  to  chemical  action  in  this  case. 

It  is  possible  that  light  may  be  thrown  on  the 
subject  of ,  the  colloid  state  by  the  study  of  the 
mutual  solubility  of  liquids.  J.  P.  Kuenen  (Phil. 
Mag.  ,6,  1903,  651)  expresses  the  opinion  that 
in  these  mixtures  and  at  the  point  of  satura- 
tion, the  molecular  conditions  set  up,  which  may 
probably  be  represented  by  a  high  molecular 


134         CHEMISTRY  AND  PHYSICS  OF  DYEING 

attraction,  make  it  impossible  for  the  solvent 
to  dissolve  more  than  a  limited  amount  of  the 
solute,  or  second  substance,  without  entering  upon 
an  unstable  condition.  If  this  is  so  with  par- 
tially miscible  liquids,  the  same  should  apply  to 
pseudo-solutions.  Beyond  the  point  of  saturation 
the  solute  will  be  in  a  state  of  abnormal  aggrega- 
tion. 

As  has  been  pointed  out  by  F.  G.  Donnan  (Phil. 
Mag.  6,  vol.  i.  647),  we  have  to  account  for  the  fact 
that  a  solid  substance  C,  when  brought  in  contact 
with  certain  liquid  media,  breaks  up,  or  disintegrates 
into  these  media,  but  in  such  a  manner  that  the  dis- 
integrating process  does  not  proceed  to  the  mole- 
cular limit. 

The  liquid  medium  seems  to  be  interspersed  with 
minute  aggregates  of  C,  which  are  still  so  much 
larger  than  their  molecular  magnitudes,  that  they 
are  subjected  to  almost  statistically  uniform 
bombardment.  These  complexes  are  such  that 
changes  of  temperature,  or  the  addition  of  compara- 
tively small  quantities  of  other  substances  frequently 
cause  the  sudden  precipitation  in  mass  of  the  sub- 
stance C. 

This  view  of  the  case  may  be  regarded,  if  we  may 
use  the  term,  as  a  very  mechanical  one.  No  provi- 
sion is  made  for  the  possible  arrangement  of  the 
system  into  aggregates  which  are  made  up  of  mole- 
cules of  both  solvent  and  solute  such  as  we  undoubt- 
edly get  in  mixtures  of  alcohol  and  water,  and  in 
many  other  cases. 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS   135 

The  first  investigator  to  study  the  solution  state 
of  the  "  direct  "  or  cotton  dyes  was  Picton  (/.C.  Soc. 
1892, 148).  He  made  use  of  certain  tests  to  establish 
the  state  of  different  solutions,  and  with  them  tested 
an  aqueous  solution  of  Congo  red. 

Tyndall  had  noticed  that  light  is  polarised  by  its 
passage  through  colloidal  solutions.  Congo  red, 
which  dissolves  easily  in  water,  was  found  under 
these  conditions  to  give  a  well-marked  polarised 
beam. 

Filtered  under  pressure  for  two  hours  through  a 
porous  cell,  the  same  solution  passed  through  practi- 
cally colourless.  A  slow  diffusion  experiment  gave 
a  similar  result. 

The  molecular  aggregation  in  aqueous  solution 
of  these  dyes  is  also  given  by  Krafft  (Ber.  1899, 
1608)  as  follows  : 

Benzopurpurin    .     3000       . .       724   (normal  calculation) 
Diamine  Blue      .     3430       . .       999  ,, 

The  following  figures  are  given  for 

Rosaniline  hydrochloride  (mol.  wt.  337) 
In  alcohol  .  .  .  330,  325,  343 
In  water  .  .  .  520,  589,  617 

Methyl  Violet  (mol.  wt.  407) 
In  alcohol  .          .          .     403.5,  421.1- 
In  water     .          .          .     804.5,  838.7,  870.4 

Methylene  Blue  (mol.  wt.  319.8) 
In  alcohol  .  .  .  321.4,  342.7 
In  water  .  .  .  321.2,  492.4,  530.5 

Tannic  Acid  (mol.  wt.  322) 
In  water     .          .          .     1587 

Picton  (ibid.}  further  pointed  out  that  the  degree 


136          CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  aggregation  in  the  case  of  Congo  red  varied  with 
its  state.  An  alkaline  solution  of  this  dye  filtered 
readily,  but  the  dye  would  not  pass  through  the 
porous  material  in  either  the  acid,  or  neutral  state. 
The  "  equalising  "  action  of  alkali  when  dyeing  with 
these  colours  may  be  explained  on  these  lines. 

It  was  also  shown  that  Magdala  red  was  not 
present  in  such  a  state  of  aggregation  in  aqueous 
solution,  but  would  pass  through  the  filter  in  neutral 
or  acid  solutions. 

With  a  solution  of  silicic  acid  the  aggregates 
were  smaller  than  in  the  case  of  Congo  Red,  for  they 
neither  polarised  light,  nor  failed  to  pass  through 
the  filter. 

There  are  indications  that  the  state  of  aggregation 
may  be  greatly  in  excess  of  that  indicated  by  Krafft 
with  the  direct  dyes. 

It  is  interesting  to  note  that  there  is  certain 
evidence  to  be  gained  from  some  experiments  on  the 
effect  of  low  temperature  on  dyes,  that  their  solution 
state  is  different  to  the  solid  one.  It  has  been  shown 
that  the  effect  of  low  temperature  on  the  colour  of 
dyes  in  the  solid  state  or  when  dyed  on  fibres  is 
nil.  On  the  other  hand,  when  in  alcoholic  solution 
some  of  them  alter  altogether,  while  others  do  not. 
This  is  a  subject  which  is  worthy  of  further  study, 
both  from  the  point  of  dyeing  and  from  that  of 
solution. 

In  the  same  way  it  is  well  known  that  the  optical 
properties  of  substances  are  modified  by  the  nature 
of  the  solvent.  For  instance,  laevo-rotatory  oil  of 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS   137 

turpentine  (37.01°  specific  rotation)  in  10  per  cent, 
solutions  gave  the  following  results  (Walker) : 

Solvent.  Specific  rotation. 

Alcohol     ....     38.49° 
Benzene  .          .          .     39-45° 

Acetic  acid        .          .          .     40.22° 


It  is  clearly  difficult  exactly  to  define  the  nature 
of  a  solution  of  a  colloid,  but  information  on  this 
point  is  being  rapidly  extended. 

It  has  been  stated  by  Henri  and  Mayer  (Compt. 
Rend.  57,  34)  that,  when  solutions  of  aniline  colours 
are  examined  ultra-microscopically,  they  exhibit  true 
colloidal  properties. 

Some  work  by  these  same  investigators  on  the 
action  of  the  /3-rays  of  radium  on  solution  of  colloids 
is  of  interest.  The  solutions  were  exposed  to  the 
action  of  these  rays  for  five  days.  Magdala  red, 
methyl  violet,  and  ferric  hydroxide  (positive)  were 
decomposed. 

On  the  other  hand,  solutions  of  aniline  blue 
and  some  other  negative  solutions  were  unaltered. 
The  action  is  said  to  be  due  to  the  negative 
charges  of  the  /3-rays  discharging  the  positively 
charged  colloids. 

The  stability  of  solutions  of  colloids  may,  in  a 
way,  be  estimated  by  their  resistance  to  centrifugal 
action.  For  instance,  Franklin  and  Freudenberger 
have  shown  that  colloidal  solutions  of  platinum  black 
and  Prussian  blue  were  completely  separated  at  a 
high  speed  from  the  solution.  The  cause  of  this 
was  attributed  to  supersaturation  effects  due 


138          CHEMISTRY  AND  PHYSICS  OF  DYEING 

to  high  acceleration  of  gravity  (Elect.  Rev.y  vol.  47, 
508).  vSuch  results  indicate,  within  certain  limits, 
the  relations  which  exist  between  the  solvent  and 
solute  in  these  special  cases.  The  conception  that  the 
precipitation  is  due  to  supersaturation  effects  is  also 
interesting,  when  it  is  remembered  that  the  same 
idea  has  been  put  forward  to  explain  the  action  of 
dyeing,  the  results  in  the  latter  case  being  attributed 
to  surface  concentration  effects. 

Otto  Weber  (Chemistry  of  India  Rubber,  page  69) 
contends  that  the  term  colloid  should  only  be  applied 
to  compounds,  the  solutions  of  which  under  all 
conditions  and  in  whatever  solvents,  behave  as 
colloids,  and  which  in  their  solutions  fully  maintain 
this  character  through  all  chemical  changes. 

As  an  absolute  definition  this  may  be  satisfactory, 
but  from  a  practical  point  of  view  it  is  not  so  unless 
we  classify  the  substances  as  follows  : 

(1)  Colloids  (as   Otto  Weber's   definition). 

(2)  Pseudo-colloids  (substances  which  enter  into 
pseudo-solutions  in  some  solvents  and   solutions  in 
others). 

(3)  Crystalloids  (substances  which  behave  with 
water  as  perfect  solutions). 

It  will  be  seen  that  on  similar  lines  no  substance 
should  be  called  a  crystalloid  unless  it  is  perfectly 
soluble  in  all  solvents,  and  in  these  solutions 
fully  maintains  this  character  through  all  chemical 
changes. 

Such  definitions,  with  our  present  knowledge,  are 
perhaps  out  of  place.  The  chief  thing  the  dyer  has 


SOLUTION  AND  THE  PROPERTIES  OF  COLLOIDS   139 

to  realise  is  the  possibility  of  the  solution  state  vary- 
ing in  the  dye  and  mordant  baths,  the  results 
which  may  be  expected  to  follow  from  these  changes, 
and  their  influence  on  the  rate  of  absorption  by  the 
fibres  introduced  into  these  baths  in  the  ordinary 
course  of  dyeing.  Also  that  the  state  of  solution 
may  be  varied  by  corresponding  variations  in  the 
physical  state  of  the  dye  liquor  brought  about  by 
altered  temperature,  concentration,  or  by  the  addition 
of  third  substances  (assistants,  &c.)  to  the  bath. 

It  is  not  advisable,  perhaps,  in  a  book  devoted  to  the 
subject  of  dyeing  from  a  more  or  less  practical  point  of 
view,  to  dwell  too  closely  on  the  theory  of  the  constitu- 
tion of  colloids  like  cellulose,  and  their  solution  state. 
This  work  is  of  great  interest  from  a  purely  theoretical 
point  of  view,  and  may  ultimately  influence  the 
practical  side  of  the  question.  It  is  too  far-reaching, 
and  perhaps  at  the  present  time  too  indefinite,  to 
be  considered  here.  That  such  ideas  should  ever  have 
been  put  forward  is,  however,  a  sign  that  the  future 
theories  which  will  be  brought  forward  to  explain 
general  reactions,  may  not  be  of  a  simple  nature,  but 
will  emphasise  the  extremely  complex  nature  of  the 
reactions  which  make  up  some  of  our  seemingly 
simple,  and  everyday  operations  in  the  dyehouse. 


CHAPTER  VII 
PHYSICAL  ACTION  AND  SOLID  SOLUTION 

THE  study  of  dyeing  from  the  physical  point  of  view 
has  served  a  purpose.  The  discussion  of  the  subject 
has  been  widened,  and  much  experimental  work 
undertaken  as  a  natural  consequence. 

In  early  days,  as  mentioned  in  chap,  i.,  such 
investigators  as  Hellot  and  Le  Pileur  d'Apligny, 
with  the  support  of  Macquer,  Berthollet,  Bergman 
and  Chevreul,  favoured  a  purely  mechanical  basis 
for  the  actions  involved. 

Hellot  in  the  year  1734  attributed  to  the  pores 
of  the  wool  fibre  the  power  of  opening  and  closing, 
and  assumed  that  the  dye  particles  lodged  in  these 
interstices.  The  astringent  substances,  which  took 
part  in  the  dyeing  operations,  were  supposed  to 
form  a  coating  over  the  colour  particles  so  fixed. 
A  colour  not  protected  in  this  way  was  assumed  to 
be  fugitive. 

The  "  invisible  mechanics  of  dyeing  "  was  due  to 
the  opening  of  the  pores  in  the  fibre,  the  deposition 
of  the  dye  particles  therein,  and  the  subesquent  action 
of  a  material  or  cement,  which  held  the  particles  in 
their  place.  He  likened  the  general  action  to  the 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       141 

very  mechanical  process  of  fixing  a  diamond  in  the 
bezel  of  a  ring.  The  hot  water  opened  the  pores, 
the  tiny  atoms  of  dye  entered,  and  the,  tartar 
and  subsequent  cooling  completed  the  operation. 

He  also  suggested  that  if  only  the  correct  astrin- 
gent could  be  found  for  the  fugitive  colours,  they, 
too,  would  be  fast.  As  it  was  they  remained  on  the 
surface  of  the  fibre,  or  were  imperfectly  fixed  in  its 
substance. 

Le  Pileur  d' Apligny  subsequently  lent  his  support 
to  this  theory,  and  extended  it  to  other  fibres,  such 
as  silk,  cotton,  flax,  &c.,  holding  that  the  mechanical 
state  of  the  different  fibres  accounted  for  the  varia- 
tion in  their  dyeing  properties.  Wool,  said  he,  was 
composed  of  a  number  of  individual  hairs  containing 
a  marrow,  or  fatty  substance.  These  fibres,  in  fact, 
were  pipes  perforated  through  their  whole  length,  and 
laterally,  with  an  infinitude  of  orifices.  By  these  the 
foreign  substances  were  admitted  to  the  central 
cavity,  after  the  removal  of  this  marrow.  In  this 
way  he  claimed  that  wool  was  the  most  porous  of  all 
fibres,  and  is,  therefore,  the  most  easily  dyed,  and  at 
the  same  time  absorbs  a  relatively  large  proportion 
of  dye  substance. 

Silk  he  considered  to  be  only  dried  animal  jelly, 
which  in  its  natural  drying  only  produces  pores  and 
inequalities  on  its  surface.  These  only  admit  colours 
in  a  dilute  form,  and  with  great  difficulty.  iThus, 
said  he,  silk  is  the  most  difficult  fibre  to  dye,  and 
cotton  stands  half  way  between  wool  and  silk.  In 
trying  to  follow  his  arguments  it  is  necessary  to 


142          CHEMISTRY  AND  PHYSICS  OF  DYEING 

remember  the  conditions  under  which  he  worked, 
and  the  dyes  at  his  command. 

In  this  way  it  was  assumed  that  dyeing  was 
purely  a  mechanical  process.  Wool  might  be  dyed  a 
scarlet  colour,  cotton  remain  colourless,  and  silk  only 
take  a  dirty  hue.  He  contended  that  the  cochineal 
tin  lake  particles  were  too  large  to  enter  the  cotton, 
or  silk  fibres,  but  that  they  would  readily  enter  the 
wool  pores.  Silk  admitted  the  impurities  because 
they  were  simple  (soluble  ?). 

He  further  pointed  out  that  this  varying  action 
might  come  into  play  even  in  the  same  fibre. 

For  instance,  the  condition  of  the  fibre  as  regards 
weaving  and  spinning  might  influence  the  result.  In 
this  way  he  explained  the  incomplete  dyeing  in  the 
interior  of  wool  dyed  with  this  scarlet  lake,  as  com- 
pared with  goods  alumed  before  dyeing.  This  ultra- 
mechanical  theory  passed  from  the  hands  of  these 
two  early  experimenters  in  a  highly  developed  state, 
and  little  seems  to  have  been  done  in  adding  to,  or 
elaborating  it  until  one  hundred  years  later. 

At  this  point,  and  under  the  altered  conditions  of 
dyeing,  the  additional  knowledge  of  the  fibres,  and 
general  science,  Walter  Crum  published  some  further 
work  on  this  subject  (J.C.S.  16.  i.  404).  This  in- 
vestigator seems  to  have  been  profoundly  impressed 
by  the  work  of  De  Saussure,  on  the  absorption  of 
different  substances  and  gases  by  charcoal,  and  he 
came  to  the  conclusion  that  several  of  the  opera- 
tions in  dyeing  were  due  to  the  capillary  action 
described  by  this  chemist,  thus  introducing  a  new 


PHYSICAL  ACTION  AND  SOLID  SOLUTION        143 

refinement  into  the  theory  at  the  end  of  this  long 
interval  of  time.  He  also  based  his  application  of 
this  theory  to  the  dyeing  of  fibres,  on  the  physio- 
logical work  of  Thompson  and  Bauer.  Their  work 
introduced  the  microscope  in  the  study  of  fibres,  and 
thus  established  a  fresh  method  of  examination.  As 
the  result  of  their  investigation  they  set  forth  the 
idea  that  the  vegetable  fibres  were  glass-like  tubes. 
After  the  ripening  of  the  fibre,  the  central  orifice, 
owing  to  the  flattening  of  the  fibre,  presented  the 
aspect  of  two  separate  tubes. 

This  next  step  in  the  mechanical  theory  was  the 
result  of  four  experimenters'  work,  and  to  the  re- 
search student  in  dyeing  this  affords  a  simple  yet 
satisfactory  example  of  the  possible  influence  of 
one  worker's  results  on  those  of  others. 

Crum  held  that  mordants  are  decomposed  in  the 
interior  of  these  tubes,  having  entered  by  the  lateral 
openings  ;  the  oxide  being  set  free  in  these  narrow 
passages  is  effectually  held  in  position.  When, 
therefore,  the  washed  cotton  passed  into  the  madder 
bath,  the  mordant  and  dye  combined  chemically  to 
form  the  dye  lake.  This  investigator  explained  the 
fixings  of  the  oxide  to  the  fibre  in  the  following  way. 
A  natural  decomposition  of  the  mordant  solution 
took  place  "  just  as  it  would  be  decomposed  in  similar 
circumstances  without  the  intervention  of  the 
cotton."  He  speaks  also  of  sacs  in  the  fibre  sub- 
stance lined  by  metallic  oxides.  The  arguments  he 
based  these  theoretical  conclusions  on  may  be  summed 
up  as  follows  : 


144          CHEMISTRY  AND  PHYSICS  OF  DYEING 

(i)  If  it  is  assumed  that  the  mordant  enters  into 
chemical  combination  with  the  fibre,  it  must  lead  to 
its  disintegration.  He  removed  the  mordant  from 
the  fibre  by  chemical  means,  and  found  that  this 
was  not  the  case. 

(2)  Under  the  microscope  the  colour  is  distributed 
on  the  internal  sides  of  the  tubes. 

(3)  The  dyeing  of  indigo  blue  supports  the  idea 
that  there  is  no  chemical  combination  in  the  proper 
sense  of  the  word  between  the  fibre  and  the  dye,  when 
the  nature  of  the  reaction  is  considered. 

Whatever  may  be  the  ultimate  place  assigned  to 
these  theoretical  considerations,  this  investigator 
introduced  a  new  method,  of  examination,  viz., 
comparison  of  the  physical  properties  of  the  fibres 
by  the  aid  of  the  microscope  before  and  after  dyeing. 

Again  we  have  a  long  interval  before  these 
ideas  were  directly  attacked,  and  disproved  in 
some  details.  De  Mosenthal  has  recently  shown 
(/.S.C.I.  23,  292)  Crum's  idea — that  the  cotton 
fibre  is  dyed  by  capillary  action — to  be  incorrect. 
Single  cotton  fibres  exhibit  no  capillary  action. 
Several  fibres  must  be  in  contact  for  the  liquid 
to  rise.  Crum's  idea  that  the  cuticle  is  non-porous 
is  also  incorrect.  It  is  very  porous.  These  ex- 
periments are  calculated  to  modify  our  ideas  on 
the  action  of  dyes  on  the  cotton  fibre,  and  to  throw 
us  back  to  the  ideas  advocated  in  the  eighteenth 
century  as  to  the  physical  nature  of  the  cotton 
fibre. 

We  now  consider  in  detail  the  many  arguments 


PHYSICAL  ACTION  AND  SOLID  SOLUTION        145 

and  experiments  brought  forward  in  favour  of  a 
simple  mechanical  theory. 

It  was  pointed  out  many  years  ago  that  neutral 
niters,  such  as  sand  in  layers,  will  remove  colouring- 
matters  and  salts  from  solutions.  Here  we  have 
large  surfaces  of  such  an  inert  substance  as  fused 
silica  retaining,  in  some  way,  or  other,  notable  quanti- 
ties of  salts,  coloured  or  otherwise.  This  filtering 
action  must  undoubtedly  be  intimately  connected 
with  surface  action. 

We  pass  on  to  the  careful  work  of  Mills  and 
Hamilton  (f.S.C.I.  1889,  263),  dealing  with  the 
action  of  mixed  colours  on  wool  and  their  relative 
absorption  by  the  fibre. 

The  colours  chosen  were  Victoria  Blue  4  R  and 
berberine  hydrochloride.  The  conditions  of  experi- 
menting were  exact.  The  temperature  chosen  might 
.have  been  higher  than  40°  C.  The  authors  indicate 
that  different  results  might  have  been  obtained  at 
95°.  The  result  arrived  at  is  expressed  in  the 
following  rule:  "  The  proportion  of  blue  to  yellow 
deposited  in  the  fibre  is  the  same  as  that  in  which 
they  existed  in  the  vat  before  dyeing." 

That  is  to  say,  the  shade  of  the  mixture  in  the 
dye-bath  remained  the  same  as  that  which  existed 
in  the  vat  before  dyeing.  The  shade  of  the  dye- 
bath  was  tested  by  the  detached  colorimeter  (Phil. 
Mag.  1879,  437). 

With  varying  quantities  of  the  colours  it  was 
found  that  the  total  quantity  of  colouring-matter 
deposited  on  the  fibre  is  least  when  the  weights  of 

zo 


146         CHEMISTRY  AND  PHYSICS  OF  DYEING 

the  blue  and  yellow  are  equal,  and  that  it  becomes 
greater  as  the  disparity  between  the  weights  in- 
creases. The  simple  mathematical  treatment  of 
finding  an  equation  for  each  of  the  dyes  separately 
was  adopted.  The  equation  was  of  the  following 
order : 

8x 


y  =  a  + 


i  -  T* 


y  being  the  reciprocal  (=  5)  of  the  total  constant 
quantity  (.2)  of  dye-stuff  taken  as  a  reagent,  and  /3 
and  a  constants  of  attraction  and  other  conditions. 
The  constant  a  represents  an  attraction  not  directly 
due  to  the  dyeing  process  as  such,  x  is  the  weight  of 
the  colour  taken,  y  the  weight  of  the  colour  de- 
posited on  the  fibre. 

The  conclusions  arrived  at  from  these  equations 
are  that  in  the  case  of  dyeing  wool  with  mixed  solu- 
tions of  these  dye-stuffs,  there  is  deposited  at  first  a 
certain  small  amount  of  dye-stuff  (x)  irrespective  of 
the  amount  of  each  dye-stuff  taken,  and  then  the 
dye-stuff  taken  up  is  proportional  to  its  own  mass, 
and  inversely  proportional  to  the  mass  of  the  other 
colours. 

The  mechanical  theory  also  receives  the  support 
of  L.  Hwass  (Farb.  Zeit.  1890-1,  224)  ;  von  Prager 
(ibid.  356),  and  Spon  (J. S.C.I.  1893,  559). 

The  assumption  is  made  that  the  dye-stuff  is  the 
same  in  the  fibre  as  in  the  free  state,  for  it  may  be 
diazotised  and  combined  with  phenols  and  amines  to 
form  azo  dye-stuffs.  The  writer  of  this  book  pointed 
out  that  this  is  not  so  in  all  cases,  or  at  any  rate, 


PHYSICAL  ACTION  AND  SOLID  SOLUTION        147 

the  "  developing  "  of  some  colours  on  silk  is  exceed- 
ingly slow;  therefore,  when  Mohlau  (Zeit.  Ang. 
Chem.  1893,  225)  shows  that  sand  will  "  dye  "  with 
naphthol  azo  colours  which  are  insoluble  in  water, 
the  case  for  a  mechanical  theory  is  on  this  point 
made  out.  The  dye  is  said  by  this  investigator  to 
enter  the  pores  of  the  silica.  The  dyeing  method 
is  as  follows  : 

(1)  Dyeing  with  /3-naphthol  dissolved  in  NaHO. 

(2)  Diazobenzene  chloride  added  to  this  solution 
after  sand  has  been  worked  in  it. 

Asbestos,  in  the  same  way  as  sand,  will  dye  in 
solutions  of  some  colours  (Spon,  Dingl.  Polyt.  f. 
1893,  287). 

It  has  been  noticed  by  Pokorng  (Bull.  Soc.  Ind. 
Mulh.  1893,  282),  that  wool  and  silk  are  able  to 
attract  from  aqueous  suspension  certain  insoluble 
amines.  All  that  is  necessary  is  that  they  shall  be 
present  in  a  state  of  fine  division.  Naphthylamine 
dissolved  in  a  small  quantity  of  alcohol  and  poured 
into  water  will  impregnate  wool  if  left  overnight. 
This  matter  will  be  further  discussed  elsewhere. 

The  fact  that  many  colours  "  rub  off  "  is  held 
to  be  in  favour  of  the  mechanical  theory,  it  being 
assumed  that  this  is  an  indication  that  the  colours 
are  not  in  chemical  combination  with  the  fibre. 

The  influence  of  temperature  on  dyeing  action 
is  a  very  important  factor,  and  may  indicate  the 
nature  of  the  reactions  which  take  place  in  the 
dye-bath.  Chemical  action,  generally  speaking,  was 
calculated  by  Hood  (Phil.  Mag.  May.  1878),  from 


148          CHEMISTRY  AND  PHYSICS  OF  DYEING 

data  obtained  from  Harcourt  and  Esson,  to  be  pro- 
portional to  the  square  of  the  temperature. 

The  results  obtained  by  Mills  and  Rennie  (f.S.C.I. 
3,  215,)  by  experimenting  with  wool,  and  dyeing 
with  rosaniline  acetate,  will  be  remembered  (see 
page  99). 

The  results  then  obtained  may  be  tabulated  as 
follows  : 

Temperature  of  dyeing.  Result. 

— i.i6°C.  . .  No  colour  deposited 

3i.n°C.  . .  Maximum  colour  deposited 

8i.i5°C.  ..  Very  little  deposited 

ioo.o°C.  '..  Fair  amount  deposited 

Hood's  law  is  not  obeyed  here.  The  reversal 
of  action  above  the  comparatively  low  temperature 
of  31°  C.  may  be  due  to  the  increasing  solubility  of 
the  dye  in  aqueous  solution. 

The  reverse  action  above  80°  C.  may  be  due  to 
the  fact  that  basic  dyes  undergo  some  change  above 
this  temperature. 

It  is  stated  that  somewhere  about  the  boiling 
temperature  rosaniline  salts  are  dissociated.  In 
weak  solutions  the  colour  is  entirely  destroyed  if 
adequate  time  be  allowed  for  this  action  (/.C.5.  35, 
38).  In  practical  dyeing  with  these  colours  very 
slight  excess  of  colour  should  be  used,  and  the 
temperature  kept  about  4O°-5o°. 

The  action  of  direct  dyes  on  cotton,  which  has 
been  a  difficulty  in  the  way  of  a  chemical  theory, 
has  been  studied  in  more  or  less  detail  by  Gnehm 
and  Kauffler  (Zeit.  Ang,  Chew,  1902,  15,  345). 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       149 

The  barium  salt  of  benzopurpurin  dyes  without 
decomposition,  and  a  similar  result  is  obtained 
with  the  sodium  salt.  The  free  acid  seems  to  dye 
equally  well  when  a  time  allowance  is  made  for  the 
decreased  solubility  of  the  same  in  water.  Similar 
results  were  obtained  in  the  case  of  benzoazurin, 
which  contains  no  amido  groups,  and,  therefore, 
cannot  form  a  salt  with  cellulose. 

A  hank  of  cotton  dyed  with  benzopurpurin 
(sodium  salt)  will  on  prolonged  boiling  with  a 
similar  but  undyed  skein,  give  up  its  dye  until  an 
equilibrium  of  colour  is  obtained  on  both  skeins. 

The  action  of  acids  on  Congo  Red  dyed  on  cotton 
is  said  to  indicate  that  the  dye  is  present  in 
the  free  state,  and  not  combined  with  the  fibre. 
Weber  stated  that  the  cellular  cotton  absorbed 
the  hot  solution  of  the  dye,  and  that  on  cooling  the 
skein  the  dye  was  precipitated.  This  is,  of  course, 
the  idea  of  some  of  the  early  investigators.  If  this 
method  of  argument  is  correct,  the  action  of  acid 
proves  equally  well  that  the  dye  is  free  in  the  case 
of  silk  dyeing,  for  the  same  effect  is  noticed  there 
with  this  dye.  It  is  interesting  to  note  that  the 
natural  moisture  in  the  cotton  fibre  is  said  to  be 
essential  to  colour-production.  If  this  is  removed 
(by  alcohol)  the  colours  are  dirty  and  dull.  It 
will  be  remembered  that  drying  does  not  seem  to 
produce  this  effect.  The  idea  that  the  benzidine 
or  direct  colours  dye  because  their  rate  of  diffu- 
sion is  less,  is  supported  by  the  same  authority. 
Croceine  3  B  will  not  dye  cotton,  but  its  barium 


150         CHEMISTRY  AND  PHYSICS  OF  DYEING 

salt  will  do  so.  Fairly  dark  shades  are  produced 
even  after  washing.  The  rate  of  diffusion  is  said 
to  be  greatly  retarded  in  this  case. 

In  1894  (J.S.C.1. 13.  95)  I  assumed  a  mechanico- 
chemical  theory  of  dyeing  to  be  the  correct  one,  a 
theory  which  depended  primarily  on  a  diffusion  pro- 
cess obeying  a  modified  form  of  the  general  laws  of 
osmosis  as  then  stated,  supplemented  by  a  chemical 
reaction  or  series  of  chemical  reactions  between 
the  fibre  and  the  dye,  Fick's  law  being  held  to 
govern  the  introduction  of  the  colour  to  the  fibre. 
Zacharias  (Farb.  Zeit.  1901,  1149)  also  brings  this  to 
notice,  and  seems  to  favour  it. 

As  I  then  pointed  out,  Fick's  law  had  been  verified 
for  gelatine  and  agar-agar  solutions.  In  the  case 
of  animal  membranes  a  retarding  action  was  noticed 
and  the  results  obtained  here  were  roughly  one 
half  those  obtained  by  the  purely  osmotic  pressure. 
The  flow  of  the  dissolved  substance  was  hindered, 
but  not  stopped,  by  the  organised  nature  of  the 
membrane. 

The  possible  influence  of  dissociation  on  the  action 
of  dyes  in  solution  must  be  considered.  Briefly,  the 
condition  of  electrolysis  in  solution  has  been  stated 
as  follows. 

Neutral  salts,  as  a  general  rule,  are  strongly  dis- 
sociated in  aqueous  "solutions.  In  dilute  solutions 
it  is  held  that  they  are  entirely  dissociated. 

The  salts  of  the  alkalies  are  very  readily  dis- 
sociated. The  acids  vary  in  their  degree  of  dis- 
sociation. Their  acid  properties  seem  to  be  due  to 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      151 

the  hydrogen  ions.     The  strongest  acids  are  those 
which  are  most  completely  dissociated. 

Water  itself  is  dissociated  to  a  small  extent,  so 
that  it  can  act  as  an  extremely  weak  acid  or  base, 
as  the  case  may  be.  Thus,  Walker  has  shown  that 
when  hydrochloric  acid  is  added  to  a  solution  con- 
taining urea,  the  acid  divided  itself  between  the 
water  and  the  base. 

Dissociation  of  dyes  may  possibly  take  place 
in  dye  solutions  of  the  ordinary  strength. 

Magenta  is  dissociated  in  water  and  alcohol. 
The  experiments  of  Fischer  and  Schmidner  with 
strips  of  blotting-paper  are  well  known.  They 
show  the  dissociation  of  double  salts,  the  salts  rising 
according  to  their  relative  rates  of  diffusion.  It 
has  been  shown  (v.  Georgievics)  that  with  magenta, 
twenty  times  the  amount  of  chlorine  necessary  for 
the  magenta  base  diffused  in  this  way.  The  exa- 
mination of  the  electrical  conductivity  of  magenta 
solutions  leads  to  the  same  conclusions  (Miolati, 
Ber.  26,  1788),  viz.,  that  dissociation  takes  place  in 
aqueous  solutions. 

It  has  been  pointed  out  by  Silbermann  (Chem. 
Zeit.  19,  1683),  that  in  any  specific  series  of  dye- 
stuffs,  increase  in  molecular  weight  is  accompanied 
by  decreased  solubility,  and  it  is  stated  that  the 
rate  of  absorption  of  the  dye  is  correspondingly 
decreased.  Assuming  that  high  molecular  weight 
means  high  molecular  volume,  the  dyes  will  take 
longer  to  diffuse  between  the  intermolecular  spaces 
of  the  fibre  and  longer  to  leave  it  also. 


152         CHEMISTRY  AND  PHYSICS  OF  DYEING 

This  does  not  seem  to  be  the  case  with  the 
primuline  colours  (Dreaper,  J.S.C.I.  1894,  95).  It 
may  be,  however,  that  the  fact  that  the  heavier 
dyes  take  longer  to  diffuse,  indicates  that  in  practice 
they  are  fixed  in  greater  proportions  on  the  external 
area  of  the  fibres.  This  might  confuse  and  obscure 
the  real  nature  of  the  reaction,  so  far  as  pure  absorp- 
tion results  are  concerned. 

Hallitt  (J.S.D.  and  C.  15,  30)  has  made  a  num- 
ber of  interesting  experiments  with  the  object  of 
explaining  the  action  of  sodium  sulphate  in  the 
dyeing  of  wool.  The  ideas  in  vogue  when  he  wrote  his 
paper  were  expressed  in  the  "Manual  of  Dyeing" 
as  follows : 

(1)  That  the  raising  of  the  temperature  in  dyeing 
by  the  addition  of  the  sulphate  increased  the  dyeing 
effect. 

(2)  The  sulphate  keeps  the  dye  in  a  fine  state  of 
suspension. 

(3)  Bisulphate  is   formed  with   the   H2SO4,  and 
as  a  consequence  the  dye  is  not  so  rapidly  trans- 
ferred to  the  fibre. 

The  fact  that  100  per  cent,  on  the  weight  of 
wool  of  sulphate  of  soda  will  only  raise  the  boiling- 
point  .75°C.  shows  that  the  effect  on  temperature  of 
the  bath  may  be  neglected  in  practice.  It  may  be 
mentioned  in  passing  that  we  have  no  knowledge  of 
the  effect  of  increased  temperature  on  dyeing  above 
100°  C.  Hallitt  does  not  consider  that  the  sulphate 
acts  by  keeping  the  dye  in  a  fine  state  of  suspension. 
He  points  out  that  acid  colours  are  more  easily 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      153 

stripped  off  wool  by  sodium  sulphate  than  by  either 
water  or  sulphuric  acid. 

Yarn  boiled  for  ten  minutes  in  the  following 
solutions  after  being  dyed  with  Carmoisine  B.  lost 
the  following  amounts  of  dye. 

Solution.  Colour  extracted. 

Water 15  %  of  total  present. 

5  per  cent.  H2SO4  .  .  .18 
50  „  Na,SO4  .  .  4.40 
50  „  NaCl.  .  .  2.40 

The  percentage  of  substances  added  is  on  the 
weight  of  yarn,  and  the  proportion  of  yarn  to  liquor 
is  1/50. 

In  some  cases  the  stripping  of  the  colour  goes  on 
beyond  the  point  of  saturation  of  the  dye  in  the 
solution.  This  remarkable  result  is  seen  when  dark 
shades  of  indigo  extract  on  wool  are  treated  in  this 
way.  The  dye  may  be  partly  thrown  out  of  solu- 
tion as  a  precipitate. 

It  is  noticed,  too,  that  an  amount  of  sodium 
sulphate  in  excess  of  that  required  to  form  the 
bisulphate  still  acts,  and  will  influence  the  dyeing. 

Uneven  skeins,  where  the  dye  is  in  patches,  will 
equalise,  if  boiled  with  a  solution  of  sodium  sul- 
phate. This  equalising  action  is  seen  when  Palatine 
Red  A  is  dyed  with 

(a)  6.8  per  cent.  HC1. 

(b)  6.8  per  cent.  HC1.  +  20  per  cent.  Na2SO4  (cryst.) 

The  first  solution  gives  a  very  uneven  result, 
and  the  second  an  even  one  on  wool  fibre.  . 

In  considering  these  experiments  with  wool  where 


154         CHEMISTRY  AND  PHYSICS  OF  DYEING 

the  dyeing  occupies  some  time  at  the  boil,  it  is  as 
well  to  remember  that  the  wool  has  an  absorbing 
action  on  the  acid.  Knecht  found  that  if  5  per  cent. 
of  acid  was  present  in  the  bath  at  the  beginning  of 
an  experiment,  only  1.5  per  cent,  remained  in  solu- 
tion at  the  end  of  the  dyeing  (J.S.D.  and  C.  1888, 
105).  These  experiments  are  said  to  indicate  that  the 
action  of  dyeing  is  equivalent  to  chemical  action 
in  dilute  solutions. 

From  this  point  of  view,  the  point  of  equilibrium 
between  the  amount  of  dye  in  the  solution  and  on 
the  fibre  is  a  movable  one.  The  addition  of  acid 
increases  the  amounts  fixed  on  the  fibre,  while  the 
addition  of  sodium  sulphate  has  the  opposite  effect. 
The  effect  produced  by  either  of  these  additions 
varies  with  different  colours. 

When  hydrochloric  acid  and  sodium  sulphate 
are  in  solution  together,  we  can  express  the  reaction 
between  them  as  follows  : 

2HC1  +  Na2S04  ^  H2SO4  +  2NaCl. 

ByGuldberg  andWaage's  law  of  chemical  action 
we  know  that  the  velocity  of  change  at  any  moment 
varies  directly  as  the  product  of  the  number  of 
equivalents  of  the  factors  of  change  present  in  unit 
volume  of  the  medium  of  change. 

The  result  arrived  at  is,  that  the  even  dyeing  of 
any  acid  is  proportional  to  its  acidic  intensity. 

An  exception  has  to  be  made  in  the  case  of 
sulphuric  acid,  which  gives  abnormal  results.  The 
intensity  values  of  acids  are  as  follows  : 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      155 


Nitric  acid 
Hydrochloric  acid 
Sulphuric  acid 
Oxalic  acid     . 
Citric  acid 
Acetic  acid 


i.oo 
i.oo 

•49 
.24 

05 
•03 


Taking  values  from  this  table,  and  with  quanti- 
ties of  acids  representing  equal  intensities,  we  obtain 
the  following  results,  one  per  cent,  of  Palatine  Red 
being  used  in  each  case. 


Acid  in  dye  bath. 

6.84  per  cent,  hydrochloric  acid 
15.62          ,,          oxalic  acid 
6.12          „          sulphuric  acid 
477.6  ,,          acetic  acid 


Colour  left  in  bath. 
.13  per  cent. 

.15 
.90 


Here  we  have  a  fairly  close  agreement,  if  we 
except  the  case  of  sulphuric  acid. 

A  possible  reason  for  this  action  is  that  the  wool 
removes  an  abnormal  amount  of  sulphuric  acid 
from  the  solution.  The  following  results  seem  to  show 
this  is  the  case. 


Per  cent,  of  acid 

Proportion  of  free  acid   Proportion  of  colour 

present. 

left  in  solution.                 left  in  solution. 

11.4  HC1. 

36.4 

.08 

5.0  HS04 

26.6 

.90 

6.1  oxalic  acid 

35-5 

•30 

23.8  acetic  acid 

60.0 

5-25 

A  much  smaller  proportion  of  sulphuric  acid  is 
left  in  the  solution.     This  action,  therefore,  may  be 


156         CHEMISTRY  AND  PHYSICS  OF  DYEING 

due  to  greatly .  decreased  mass  action.  The  chief 
action  of  acids  has  been  said  to  be  on  the  wool  fibre 
itself.  Knecht  has  shown  that  wool  treated  with 
acid  and  washed  to  neutrality,  dyes  well  in  a 
neutral  solution  of  colour  acid. 

This  matter  is  not,  however,  clear.  If  the  sul- 
phuric acid  is  taken  up  in  abnormal  quantities,  it 
would  follow  that  the  fibre  is  more  acted  on  in  this 
case,  and,  therefore,  other  things  being  equal,  the 
dyeing  should  be  more  complete. 

It  is  clear,  at  any  rate,  that  the  direct  action 
of  the  acid  is  modified  in  some  way  by  the 
presence  of  sodium  sulphate  or  sodium  chloride. 
Sodium  sulphate  is  one  of  the  products  of  the  direct 
change  which  takes  place  between  colour  acid  and 
salt,  and  by  largely  increasing  its  mass  in  the  solu- 
tion by  direct  addition,  the  point  of  equilibrium  is 
pushed  back,  and  more  free  acid  remains  in  solution. 

Therefore,  by  the  addition  of  sulphate  the  dye 
is  stripped  from  the  fibre.  The  facts  seem  to  be  in 
accordance  with  the  laws  of  equilibrium. 
„  _The  colour  acids  of  Scarlet  2R  and  Orange  G  will 
dye  wool  very  feebly.  In  fact,  they  are  said  hardly 
to  stain  the  fibre  at  all,  and  in  the  former  case  not 
so  deeply  as  its  sodium  salt. 

An  addition  of  3  per  cent,  sulphuric  acid  will 
drive  on  a  large  proportion  of  these  dyes,  and  3  per 
qent.  hydrochloric  acid  will  exhaust  the  bath. 

With  Cardinal  red  the  colour  acid  gives  a  better 
result.  In  this  case  about  half  the  dye  goes  on  to 
the  fibre  without  the  addition  of  any  acid. 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      157 

This  research,  which  is  clearly  of  interest  to  the 
wool  dyer,  is  also  of  equal  interest  in  other  ways. 
It  is  an  example  of  the  work  that  might  be  done  in 
our  dyeing  colleges  if  some  definite  scheme  for 
technical  research  was  adopted.  -  ; 

The  effect  of  varying  temperatures  of  the  dye- 
bath  may  be  mentioned  here. 

We  have  seen  the  extreme  importance  of  tem- 
perature in  mordanting,  and  how  this  varies  with 
the  fibre.  Silk  and  cotton  give  the  greatest  effect 
in  the  cold  (except  when  tannic  acid  is  used  as 
mordant). 

The  dehydrating  effect  of  a  high  temperature 
in  dyeing  on  some  mordants  may  even  prevent  the 
formation  of  a  lake,  as  has  been  pointed  out  in 
dyeing  cotton  with  alizarine;  and  every  dyer  ex- 
perienced in  dyeing  alizarine  on  alumed  silk  will 
have  noticed  the  same  effect. 

The  action  of  tannic  acid  on  animal  fibres  and 
substances  generally  is  an  important  one.  There 
are  dye-houses  in  the  south  of  France,  and  else- 
where, entirely  devoted  to  dyeing  silk  black  with 
tannin  extracts  on  mordants.  Before  the  intro- 
duction of  the  direct  dyes  tannic  acid  was  very 
largely  used  in  mordanting  cotton  for  basic  colours. 

Its  action  in  the  case  of  tanning  leather  is  well 
known.  The  tannin  is  said  to  combine  with  the 
material,  reducing  its  permeability  by  water  and 
modifying  it  in  other  ways. 

A  similar  action  is  noticed  with  silk.  Gallic  acid 
is  not  absorbed jto  the  same  extent  as  tannic  acid, 


158          CHEMISTRY  AND  PHYSICS  OF  DYEING 

although  a  process  proposed  some  time  ago  for  the 
separation  of  these  two  acids  by  absorption  by 
silk  is  of  little  value. 

Gallic  acid  will  not  precipitate  so  soluble  a  pro- 
teid  as  gelatin,  but  in  the  presence  of  tannic  acid 
both  acids  are  carried  down. 

Tannic  acid  is  absorbed  by  cotton,  but  gallic 
acid  is  not  under  ordinary  circumstances.  It  is  not 
known  whether  it  is  absorbed  in  the  presence  of 
tannic  acid. 

Tannic  acid  is  absorbed  by  cellulose  in  its  various 
forms  as  follows  (Knecht,  J.S.D.  and  C.  1892,  40) : 

Form  of  cellulose.  Tannic  acid  taken.      Tannic  acid  absorbed. 

Bleached  cotton   .  .       .25  grms.       . .       .0513  grms. 

Unbleached  cotton  .  do.  . .       .0563       „ 

Mercerised  cotton  .  do.  ..       .1033       „ 

Pptd.  cellulose      .  .  do.  ..       .1525 

Further  work  on  this  subject  has  been  done  by 
Gardner  and  Carter  (f.S.D.  and  C.  1898,  143),  and 
the  relative  action  of  tannic  and  gallic  acids  on 
cotton  confirmed.  The  theory  that  absorption  is 
mainly  due  to  physical  action  is  not  considered 
by  these  investigators  to  be  supported  by  the  fact 
that  the  regenerated  or  precipitated  cellulose  has  an 
increased  affinity  for  tannic  acid.  On  the  other 
hand,  the  acid  is  easily  removed  by  cold,  or  boiling 
water. 

The  action  may  be  of  a  secondary  nature,  and 
the  water  replace  the  tannic  acid  by  mass  action. 

A  series  of  experiments  with  different  aromatic 
phenols  was  made  with  the  following  results,  the 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      159 

conditions  of  the  experiments  being  as  follows  : 
Strength  of  solution  I  grm.  per  litre;  10  grms.  of 
cotton  were  soaked  in  this  for  three  hours.  The 
percentage  of  substance  absorbed  is  given  in  each 
case. 

Reagent.     l   x. 


OH 


Gallotannic  acid 


Catechutannic  acid 


Gallic  acid 


Pyrogallol 


Phloroglucinol 


Protocatechuic  acid 


COOH 


OH 


OH 
OH 


OH 


Pyrocatechol 


Resorcinol 


Percentage 
absorbed. 


4-5 


24-26 


\/ 


OIL 


45-50 


166         CHEMISTRY  AND  PHYSICS  OF  DYEING 

OH 

CO.OH 


Salicylic  acid 


Guaiacol 


t  CH(OH).COOH  7-8 

Mandelic  acid 


OH 

0(CH3) 


The  difference  between  the  absorption  of  tannic 
and  gallic  acids  is  very  marked. 

The  difference  between  the  1.2.3  trihydroxy- 
benzene  and  the  1.3.5  compound  is  also  noticeable. 

The  different  results  obtained  with  the  1.2  and 
1.3  dihydroxybenzenes  is  still  more  marked  and,  if 
it  were  not  that  the  suggestion  is  negatived  by  the 
figures  for  pyrogallol,  would  indicate  that  the  meta 
position  has  some  influence  on  the  absorption  factor. 

A  general  survey  of  these  effects  of  the  OH  and 
COOH  groups  on  the  rate  of  absorption  makes  it 
difficult  to  imagine  that  the  action  is  a  chemical 
one.  There  is  no  question  here  of  a  phenol  combin- 
ing in  some  way  with  a  diazonium  compound. 
Kcechlin  found  that  cotton  saturated  with  tannic 
acid  in  a  50  grm.  per  litre  solution  was  still  able 
to  absorb  tannic  acid  from  a  20  grm.  solution.  It 
retained  the  whole  of  its  tannic  acid  in  a  5  grm. 
solution,  and  only  began  to  lose  it  when  the  strength 
was  reduced  to  2  grms.  This  action  is  discussed 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      161 

elsewhere.     The  action  seems   to   be   reversible   in 
this  case. 

The  effect  of  the  addition  of  fatty  acids  to  the 
tannic  acid  solution  is  as  follows : 

Solution.  Absorbed. 

Tannic  acid  alone  (as  above)  .  .  32  per  cent. 

+   formic  acid  .  .  48-50  ,, 

+   acetic  acid  .  .  48-50  ,, 

+   propionic  acid  .  .  48-50  ,, 

The  acids  were  present  in  quantities  equivalent 
to  4.5  grm.  acetic  acid  per  litre.  From  a  chemical 
point  of  view  the  increased  absorption  of  one  acid 
in  the  presence  of  another  is  an  abnormal  one. 

With  stronger  acids  this  ratio  does  not  hold,  as 
the  following  figures  will  show. 

Solution.  Absorbed. 

Tannic  acid  alone       .         .  .  .           32  per  cent. 

+   acetic  acid  .  .  48-50           „ 

+   citric  acid  .  .  19-21           ,, 

+   tartaric  acid  .  .  20-22           ,, 

+  sulphuric  acid  .  .  18-20          „ 

+   hydrochloric  acid  .  30-32  ,, 

+   sodium  acetate  .  16-18  „ 

The  effect  of  varying  the  percentage  of  acetic 
acid  on  a  solution  of  tannic  acid  (i  grm.  to  litre)  is 
as  follows  : 

Acetic  acid  per  litre.  Tannic  acid  absorbed. 

0  grms.    ....     30-32  per  cent. 

1  „       •         *         ...     35-36 

2  „     ..  V        .     40-42 
5       „       .  -     49-51 

10     „     H     .       ;      .    32-34 

20       „       ;        .  .     31-32 

II 


i6a         CHEMISTRY  AND  PHYSICS  OF  DYEING 

This  rather  negatives  the  idea  that  the  action 
of  the  acetic  acid  is  on  the  fibre  rather  than  on  the 
acid  in  solution. 

An  action  of  a  similar  order  is  noticed  in  the 
case  of  gallic  acid  (i  grm.  per  litre). 

Acetic  acid  per  litre.  Gallic  acid  absorbed. 
.o  grms.    .  .     o      per  cent. 

•5       „       •  •  •         .2 

2-5       „       •  •  .'.-        ..    8.5 

5          „     '  •  .  .        -7-5 

25         „       .  •  .  ;   .    5-5 

These  results  should  be  extended  to  the  animal 
fibres,  and  to  precipitated  cellulose  (artificial  silk). 
They  are  of  great  interest  from  a  theoretical  as  well 
as  from  a  practical  point  of  view.  The  influence  of 
the  addition  of  acetic  acid  to  the  solutions  is  clearly 
shown  in  the  'following  curves,  the  figures  being 
taken  from  the  above  results. 


o 


o   o 


0  ' No.  i 


No.  2 


5  10  15  20  25  grms. 

Acetic  Acid" per  litre 

ABSORPTION    OF    TANNIC    AND    GALLIC    ACIDS    IN    PRESENCE    OF 
ACETIC    ACID 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      163 

These  curves  show  clearly  the  influence  of  the 
addition  of  acetic  acid  on  the  absorption  of  tannic 
and  gallic  acids  by  cotton.  The  concentration  of 
the  aromatic  acid  was  in  each  case  i  grm.  per  litre, 
and  the  acetic  acid  was  added  up  to  a  strength  of 
25  grms.  per  litre. 

The  reversal  in  the  action  is  clearly  seen  in  both 
cases,  and  occurs  at  a  comparatively  early  stage. 

Perhaps  the  influence  is  the  more  pronounced 
in  the  case  of  gallic  acid,  for  in  this  case  the  amount 
of  acid  absorbed  in  the  absence  of  acetic  acid  is  said 
to  be  nil. 

The  absorption  of  gallic  acid  by  a  tannic  acid 
collin  (soluble  gelatine)  coagulum  gives  figures 
which  do  not  correspond  with  the  above  results. 

The  curves  on  p.  164  (Dreaper  and  Wilson, 
Proc.  Chem.  Soc.  1906,  22,  70)  indicate  generally 
the  influence  of  the  presence  of  salts  and  acids  on 
the  amount  of  gallic  acid  absorbed.  Curve  No.  i 
shows  the  increase  in  the  gallic  acid  absorbed  as  the 
amount  of  tannic  acid  increases  when  the  collin  is 
added  to  the  mixed  acids.  When  the  gallic  acid  is 
added  after  precipitation  the  result  is  practically  the 
same.  Nos.  2  and  3  indicate  the  increased  absorption 
in  the  presence  of  sodium  and  ammonium  chlorides, 
Nos.  4  and  5  the  decreased  absorption  in  the  pre- 
sence of  hydrochloric  and  acetic  acids  respectively. 

Gelatin  in  the  hydrogel  state  absorbs  gallic 
acid,  although  no  coagulation  takes  place  when 
these  two  substances  in  solution  are  mixed  together. 
Salts  increase  this  absorption  and  alcohol  reduces  it. 


164          CHEMISTRY  AND  PHYSICS  OF  DYEING 

Albumin  absorbs  gallic  acid  when  precipitated  by 
tannic  acid  or  heat.  Alcohol  prevents  this  action 
and  also  the  absorption  of  tannic  acid.  In  very  con- 
centrated solutions  gallic  acid  precipitates  albumin. 


No.   i 


No.  2 

No.  3 


No.  5 


No.  4 
Addition  of  Reagents 

ABSORPTION    OF    GALLIC    ACID    BY    COLLOIDS 

Similar  results  were  obtained  when  silk  or  hide 
powder  took  the  place  of  albumin,  and  there  seems 
to  be  a  great  similarity  in  the  reactions  with  these 
different  organic  colloids — the  curves,  so  far  as  they 
go,  indicating  that  the  taking  up  of  tannic  and 
gallic  acids  by  organic  colloids  is  chiefly  a  matter  of 
absorption. 

The  writer  has  pointed  out  that  as  osmosis 
probably  plays  an  important  part  in  the  process  of 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       165 

dyeing,  it  might  be  possible  to  institute  experiments 
comparing  the  relative  osmotic  pressure  of  dyes 
through  inert  membranes  on  the  one  hand  and 
fibres  on  the  other. 

Whatever  the  ultimate  process  of  dyeing  may  be, 
it  seems  necessary  to  assume  that  the  dye  enters 
the  fibre  substance  by  direct  diffusion. 

As  I  then  pointed  out,  the  general  laws  of  diffu- 
sion would  probably  govern  this  method  of  intro- 
duction, although  it  must  be  remembered  that  these 
will  only  apply  to  substances  in  a  more  or  less  perfect 
state  of  solution.  The  laws  are  as  follows  : 

(1)  The    pressure    (osmotic)    is    proportional    to 
the  concentration  of  the  solution,  or  proportional 
to  the  volume  in  which  a  definite  mass  of  the  sub- 
stance is  contained.     This  law  only  holds  good  for 
inert  substances. 

(2)  The  pressure  increases  for  constant  volu    e 
proportionately  to  the  absolute  temperature. 

(3)  Quantities   of   substances   (dissolved)   which 
are   in  the  ratio  of   the   molecular  weights   of   the 
substances  exert  equal  pressure  at   equal   tempera- 
tures. 

It  should  not  be  impossible  to  find  whether  the 
dyeing  action  is  in  conformity  with  these  laws,  or 
is  complicated  by  further  reactions  as  indicated 
elsewhere. 

The  present  state  of  our  knowledge  does  not 
supply  figures  which  are  available  for  this  investi- 
gation. As  mentioned  elsewhere,  it  is  known  that 
animal  fibres  materially  modify^this  process.  The 


166         CHEMISTRY  AND  PHYSICS   OF  DYEING 

results  obtained  are,  roughly,  half  those  obtained 
by  the  true  osmotic  pressure,  when  exhibited  in  the 
case  of  solutions  of  agar-agar  or  gelatine. 

It  would  seem  from  the  above  recorded  experi- 
ments with  tannic  and  gallic  acids,  that  the  absorp- 
tion of  the  latter  acid  was  as  perfect  when  the 
coagulum  of  tannic  acid  and  collin  was  first  formed 
as  when  the  gallic  acid  was  actually  present  at  the 
time  of  formation.  The  rate  of  diffusion  in  the 
former  case  is  therefore  very  rapid  and  complete. 

Fick's  law  "  that  the  quantity  of  salt  which 
diffuses  through  a  given  area  is  proportional  to  the 
difference  between  the  concentration  of  the  two 
areas  infinitely  near  to  each  other,"  was  found  not 
to  be  true  for  animal  membranes.  An  osmotic 
pressure  exists,  but  it  does  not  reach  its  true  value 
(Zeit.  /.  Phys.  Chem.,  3,  316). 

It  is  clear  that  the  fibre  substance  must  be  per- 
meable in  order  that  dyeing  may  take  place ;  this  is 
indicated  by  the  fact  that  nitrocellulose  in  the  fibre 
state  will  dye  readily,  but  when  ,in  the  state  of  a 
film  (prepared  by  dissolving  in  acetone)  it  will  not 
do  so,  or  at  any  rate  the  action  is  a  very  slow  one. 

The  dyeing  of  wool  may  be  prevented  by  treat- 
ment with  sulphuric  acid,  hypochlorite  of  soda,  and 
stannous  chloride  (Fr.  Pat.,  318741).  So  that  here 
we  have  a  mineral  acid,  an  oxidising  agent,  and  an 
acid  reducing  reagent  acting  in  the  same  direction,  so 
far  as  colour  absorption  is  concerned. 

The  action  of  solvents  for  dyes  on  dyed  fabrics 
also  gives  interesting  results. 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       167 

This  action  is  noticed  in  other  parts  of  this 
book.  Most  colouring-matters,  acid,  basic,  or  direct, 
and  even  the  mordant  and  developed  colours  are 
all  said  to  be  soluble  in  either  go  per  cent,  acetic 
acid,  or  absolute  alcohol,  if  not  in  the  cold,  at  any 
rate  when  heated. 

It  is  an  interesting  fact  that  some  of  the  acid 
colours  on  wool  will  not  yield  to  alcohol,  but  will 
readily  leave  the  fibre  if  a  small  quantity  of  water 
is  added  (Pokorng,  Bull.  Soc.  Ind.  de  Muhl.  1902, 245). 

This  may  be  due  to  the  fact  that  absolute  alcohol 
cannot  penetrate  the  wool  substance.  When  a  small 
quantity  of  water  is  present  the  fibre  substance 
becomes  sufficiently  hydrated  for  the  spirit  to  enter. 

Patent  Blue  and  New  Crocein  are  examples  which 
will  illustrate  this  action. 

The  successive  action  of  90  per  cent,  acetic  acid 
and  spirit  will  remove  almost  any  colour. 

In  the  case  of  cotton  it  would  seem  that  the 
structure  of  the  fibre  will  allow  of  the  action  of 
other  liquids  than  water. 

It  is  recorded,  for  instance,  that  alizarine  lakes 
dissolved  in  alcohol-ether  will  dye  cotton.  It  is 
not  known,  however,  if  silk  and  wool  will  dye  in 
this  solution. 

Amyl  alcohol  will  apparently  act  in  the  same 
way.  Rosaniline  dyed  on  silk  from  an  aqueous 
solution  is  partly  soluble  in  this  solvent,  and  an 
equilibrium  is  said  to  be  established  between  the 
dye  in  solution,  and  the  dye  on  the  fibre  (Sisley, 
Bull.  Soc.  Chem.  1900). 


168          CHEMISTRY  AND  PHYSICS  OF  DYEING 

Solid  Solution. — The  phenomenon  of  solid  solu- 
tion was  first  noticed  by  van't  Hoff  in  1890  (Zeit. 
f.  Phys.  Chem.  5,  322).  This  idea  of  the  solution 
of  one  solid  in  another  was  brought  forward  to  explain 
certain  facts  recorded  in  connection  with  alloys,  and 
salts  of  similar  molecular  constitution,  or  structure. 

The  suggestion  that  solid  solution  might  be  a 
universal  phenomenon  was  not  put  forward,  but 
that  sodium  sulphate  and  potassium  sulphate,  or 
silver  and  lead  respectively,  were  capable  of  dis- 
solving one  another  under  certain  conditions. 

Witt,  in  1890  and  1891,  advanced  the  hypothesis 
that  dyeing  might  be  a  case  of  solid  solution. 

If  this  were  so,  the  range  of  solid  solution  must 
be  widened  to  include  the  solution  of  various  in- 
organic and  organic  substances  in  the  fibres.  The 
idea  presented  here  is  that  the  dye-stuffs  are  not 
only  held  by  the  fibre  substance,  but  actually  enter 
into  solution  in  it. 

The  dye  in  the  fibre  was  considered  to  be  in  the 
same  state  as  the  oxides  which  are  soluble  in  precious 
stones  (Farb.  Zeit.  2,  1-6).  Witt  considered  that 
the  fact  that  fibres  are  red,  and  not  bronze  green, 
when  dyed  with  magenta,  and  blue,  and  not  bronze 
green  when  dyed  with  aniline  blue,  supported  this 
idea.  Rhodamines,  also,  will  only  fluoresce  in  solu- 
tions, and  they  do  so  on  fibres.  That  magenta  is 
taken  up  by  silk  would  be  explained  by  its  being 
more  soluble  in  it  than  in  water.  If  a  solution 
(alcohol)  in  which  the  dye  is  more  soluble  be  taken, 
the  fibre  will  not  dye  to  the  same  extent. 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       169 

The  effect  of  trying  to  dye  cotton  with  magenta 
may  be  likened  to  the  action  of  benzene  on  a  solution 
of  resorcinol  in  water.  The  relative  solubility  of  the 
latter  is  so  much  in  favour  of  the  water  that  the 
benzene  cannot  absorb  it.  On  the  other  hand,  ether 
is  able  to  do  so,  and  removes  the  resorcinol.  In 
this  way  the  action  of  the  ether  is  compared  to 
that  of  silk.  The  benzene  may,  in  the  same  way, 
be  compared  to  the  cotton  fibre. 

Again,  amyl  alcohol  may  be  compared  with  a 
phase  where  the  dye  is  imperfectly  removed  from 
the  dye-bath,  for  it  only  partly  removes  the  resor- 
cinol from  aqueous  solution. 

The  wreak  point  in  this  argument  is  the  in- 
discriminate way  in  which  ordinary  solution  and 
solid  solution  are  assumed  to  be  similar  in 
nature  so  far  as  their  actions  are  concerned,  and 
the  universal  nature  of  the  interchange.  This  is 
not  in  accordance  with  the  recognised  theory  of 
solid  solution,  nor  have  any  facts  been  brought 
forward  which  would  allow  of  such  an  arbitrary 
extension  of  this  theory  to  cover  the  reactions  which 
take  place  in  dyeing. 

It  is  considered  also  that  the  different  shades 
given  by  the  same  dye  to  different  fibres  may  be 
explained  by  solution.  Isonitrolic  acid,  which  is 
colourless,  dissolves  in  benzene  with  a  blue  colour. 
Why  should  not  the  changes  in  dyeing  be  due  to  a 
similar  condition  ?  The  action  of  dyeing  in  the 
case  of  adjective  colours  is  said  to  be  similar  to  the 
action  of  benzene  to  which  benzoyl  chloride  has  been 


170          CHEMISTRY  AND  PHYSICS   OF  DYEING 

added.     The  resorcinol  in  this  case  is  taken  up  by 
the  water. 

It  may  be  gathered  from  this  statement  that 
Witt  even  suggests  that  the  adjective  colours  are 
soluble  in  the  mordants.  If  this  is  so,  we  must 
assume  that  no  definite  chemical  combination  takes 
place  between  the  mordant  and  dye,  and  that  the 
definite  lakes  isolated  by  Liechti  do  not  exist. 

The  weak  points  in  the  above  argument  have 
been  pointed  out  by  v.  Georgievics  (/.5.C.7.,  xiv. 
149). 

Magenta  finely  powdered  and  mixed  with  chalk 
gives  a  red,  and  not  a  bronze  colour.  If  the  crystals 
are  rubbed  between  glass  plates,  the  same  result  is 
noticed.  The  colour  of  the  crystals  is,  therefore, 
shown  not  to  be  the  natural  colour,  but  an  abnormal 
one,  due  to  the  dispersion  of  the  light  on  the  surface 
of  the  crystals  or  thick  layers.  If  wool  be  dyed 
with  a  very  concentrated  solution  of  magenta  it 
bronzes. 

Fluorescence  is  held  to  be  possible  in  the  solid 
state.  Fluorspar  and  barium  platinocyanide  are 
notable  examples  of  this.  Silk  dyed  with  rhoda- 
mine  is  fluorescent,  wool  is  not.  Is  the  first  an 
example  of  solid  solution,  and  the  second  not  ? 
Fluorescence  in  fibres,  it  is  contended,  is  due  to  a 
surface  action. 

If  the  dyeing  of  wool  is  due  to  selective  solution 
it  should  be  correspondingly  reversible.  This  is  not 
the  case  with  many  dyes.  Also,  if  wool  takes  up 
more  colour  at  100°  C,  the  dye  should  be  more 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       171 

soluble  at  that  temperature,  and  consequently  might 
be  expected  to  give  up  its  dye  again  to  water  at  a 
lower  temperature. 

The  fact  that  the  structure  of  the  fibre  also 
plays  some  part  in  the  reaction  is  also  against  this 
theory. 

On  a  later  occasion  (Monatsh.  filr  Chem.  25, 
705)  v.  Georgievics  gives  the  results  of  experiments 
with  indigo  carmine,  varying  the  ratio  of  fibre  to 
solution,  concentration,  and  amount  of  sulphuric 
acid  present,  singly,  and  in  pairs. 

The  following  law  was  found  to  express  the 
results  obtained : 


,/cw 

~~cs~ 

CW  =  dye-stuff  in  100  cc.  after  the  process  of  dyeing. 
CS  =  dye-stuff  in  100  grms.  silk  after  the  process  of  dyeing. 

This  would  agree  with  the  requirements  of  van't 
Hoff  and  Nernst's  modification  of  Henry's  law  of 
solution,  and  it  would  follow  that  the  dye-stuff 
exists  in  silk  in  a  simpler  molecular  condition  than 
in  water.  With  concentrated  solutions  the  value 


increases.     This  would  point  to  the  presence 

of  more  complex  molecules  in  solution.  In  spite  of 
these  results  the  non-reversibility  of  the  process  is 
against  a  theory  of  solid  solution.  The  writer  of 
this  book  has  given  figures  showing  the  extra  fast- 
ness of  dyes  dyed  ingrain  over  the  same  colours 
dyed  direct,  in  terms  of  their  resistance  to  the 
action  of  boiling  soap  solution.  This  result  seems 


172         CHEMISTRY  AND  PHYSICS  OF  DYEING 

to  be  a  general  one,  and  extends  over  the  dyeing  of 
silk,  wool  and  cotton. 

These  results  are  very  difficult  to  explain  by  the 
solid  solution  theory.  No  explanation  can  be  given 
which  will  explain  this  difference  in  "  solubility.'' 

It  has  been  claimed  that  the  abnormal  action 
of  jute  fibre  (lignocellulose)  on  ferric  ferricyanide 
solution  supports  the  solid  solution  theory  (Cross 
and  Bevan,  J. S.C.I.  12,  104).  If  such  a  solution 
be  prepared  by  mixing  equal  parts  of  N/2O  ferric 
chloride  and  potassium  ferricyanide  solutions,  and 
the  fibre  be  soaked  in  this  colourless  solution,  it  is 
dyed  a  dark  blue  shade,  and  gains  20-50  per  cent, 
in  weight.  Under  the  microscope  the  fibre  appears 
an  intense  transparent  blue,  exhibiting,  it  is  claimed, 
all  the  characteristics  of  solid  solution. 

This  is  possibly  not  a  correct  assumption  ;  the 
ferric  ferricyanide  may  be  present  in  the  colloid 
state.  Jute  fibre  will  not  absorb  the  oxide  from  ferric 
chloride  solution  alone  (only  0^4  per  cent.).  The 
small  amount  fixed  is  partially  reduced.  The 
absorption  of  oxide  from  a  ferric  chloride  solution 
by  a  fibre  would  be  an  extraordinary  one.  The 
authors  are  perhaps  straining  a  point  in  arguing 
from  the  ferric  chloride  solution  to  the  ferric  ferri- 
cyanide one. 

They  claim  that  the  action  in  the  case  of  the  ferric 
ferricyanide  is  a  specific  one,  and  contend  that  the 
necessary  reduction  to  the  ferrous  state  takes  place 
in  the  fibre,  and  not  in  the  solution.  It  is  argued 
that  the  fibre  precipitates  the  ferricyanide,  and  that 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       173 

this  is  followed  by  a  rearrangement  of  its  constitu- 
ents and  production  of  the  blue  compound. 

A  solution  of  gelatine  was  found  to  precipitate 
this  ferric  salt  in  an  almost  quantitative  way.  This 
may  confirm  the  writer's  opinion  that  the  ferric 
ferricyanide  is  present  in  the  colloid  form,  and  not 
in  a  state  of  solution  as  supposed  by  Cross  and 
Bevan. 

As  the  jute  fibre  contains  an  aldehyde  group, 
and  a  lignone,  or  quinone  containing  a  CO  group 
and  OH  groups  with  phenolic  functions  (Chem. 
Soc.-J.  55,  199),  it  is  contended  that  this  will  account 
for: 

(i)  The  deoxidation  of  Fe'" ;  (2)  union  of  ferric 
and  ferrous  oxides;  (3)  combination  with  HCN. 

The  authors  do  not  consider  that  dyeing  can  be 
of  such  a  simple  nature  as  Vignon  assumes,  viz., 
the  interaction  of  groups  of  opposite  nature  (acid 
and  basic). 

So  far  as  the  colour  is  concerned,  they  assume 
that  in  the  complicated  cyanide  we  have  to  do  with 
a  C6  ring  and  a  quinoid  constitution.  This  falls  in 
with  Armstrong's  theory  of  colour  (Proc.  Chem. 
Soc.  1888,  27  ;  1892,  101). 

Returning  to  this  subject  when  criticising  two 
papers  attacking  the  solid  solution  theory  (Weber, 
J.S.C.1. 13, 120 ;  andDreaper  13,96),  Cross  and  Bevan 
(/.S.C.I.  13,  354)  deny  that  the  reduction  and  fixing 
is  caused  by  contact  action  with  the  aldehyde  groups 
of  the  fibre,  and  they  distinguish  between  the 
process,  which  may  be  chemical,  and  the  product, 


174          CHEMISTRY  AND  PHYSICS  OF  DYEING 

which  is  a  solid  solution.  The  authors  consider 
that  in  the  dyed  fibre  the  state  of  the  dye  is  one 
of  dissociation  or  molecular  simplification,  similar 
to  that  known  to  prevail  in  gases.  At  any  rate,  in 
dilute  solutions  they  regard  the  action  of  dye  and 
fibre  as  a  case  of  ordinary  solid  solution.  Magenta 
can  be  dissociated  in  solution  by  prolonged  heating, 
but  with  a  complete  loss  of  colour.  They  also 
consider  that  the  extreme  sensitiveness  of  diazotised 
primuline  produced  in  the  fibre  is  a  result  of 
solution. 

In  a  fully  developed  ingrain  dye  they  consider 
that  we  have  a  chemical  bond  of  union  between  the 
dye  and  fibre.  The  fact,  however,  that  this  diazo- 
tised primuline  "  is  capable  of  further  synthesis  to 
produce  ingrain  colours  is  one  of  the  essential  fea- 
tures of  solution  as  opposed  to  chemical  action." 
Why  this  is  so  they  do  not,  however,  explain.  It  is 
even  known  (Dreaper,  J.S.C.I.  13,  96),  that  in 
some  cases  this  action  of  developing  cannot  take 
place.  There  seems  to  be  as  much  evidence  for,  as 
against  this  proposition. 

While  arguing  that  dyeing  is  a  matter  of  solution 
they  hold  that  the  molecular  configuration  of  the 
reagents  plays  a  part.  One  of  the  principal  arguments 
against  the  solid  solution  theory  is  that  solid  solution 
is  practically  impossible  when  the  varied  nature  of 
these  reagents  is  taken  into  account. 

Their  contention,  too,  that  the  action  is  aided 
by  the  presence  of  salt-forming  groups  (chiefly  OH), 
modified  by  the  groups  with  which  they  are  in 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       175 

proximate  or  immediate  contact,  at  once  brings  us 
back  to  the  chemical  theory,  and  with  this  the  need 
of  a  solid  solution  theory  vanishes. 

We  here  have  a  singular  division  of  the  action 
of  dyeing ;  and  solid  solution  relegated  to  the  product 
to  the  exclusion  of  the  process  of  dyeing,  which  may 
be  either  physical,  or  chemical. 

The  claim  made  by  Weber  that  once  grant  a 
chemical  action,  and  the  solid  solution  theory  is  no 
longer  required  to  explain  the  action  of  dyeing, 
seems  a  reasonable  one.  The  claim  that  the  sub- 
stance in  solid  solution  is  different  from  the  one  in 
solution  is  an  arbitrary  one. 

Weber  contended  that  the  differentation  between 
the  process  of  dyeing,  and  the  final  state  of  the  dye 
"  contains  all  the  elements  of  a  scientific  abortion/' 
Furthermore,  that  the  writer's  investigations, 
coupled  with  his  own  (above),  lead  to  "an  un- 
conditional rejection  of  the  solid  solution  theory 
as  proposed  by  O.  N.  Witt." 

It  is  of  interest  to  note  that  S.  E.  Sheppard 
(Photo.  Journal,  1903,  271)  holds  that  the  colour 
sensibility  of  silver  haloids,  when  treated  with  certain 
dyes,  is  due  to  the  formation  of  loose  compounds  of 
the  dye  and  the  haloid.  The  extra  sensitiveness  of 
these  silver  salts  to  the  action  of  certain  rays  of 
light  might  be,  in  a  way,  comparable  to  the  results 
obtained  with  primuline  diazotised  in  situ. 

The  results  obtained  by  Walker  and  Appleyard 
(J.C.S.  1896,  1334)  with  picric  acid,  and  its  dis- 
tribution between  water  and  silk,  do  not  confirm 


176         CHEMISTRY  AND  PHYSICS  OF  DYEING 

v.  Georgievics'  experiments  with  indigo  carmine,  or 
at  any  rate,  do  not  agree  with  them. 
In  this  case  they  found  that 


Here  we  have  a  case  where  the  simple  rule  is  not 
followed,  which  it  would  be  if  the  molecular  state 
were  the  same  in  both  solvents.  The  solid  solution 
theory  requires  that  the  ratio  of  dye  in  solution  to 
that  in  the  fibre  will  be  a  constant  irrespective  of 
concentration. 

If,  however,  the  molecular  weight  is  n  times  as 
great  in  the  one  solvent  as  in  the  other,  then  the 
nih  root  of  the  concentration  in  the  first  solvent  will 
have  a  constant  ratio  to  the  concentration  in  the 
other  solvent. 

In  the  latter  case 

c~T 

_     TT 

cw 

will  apply. 

Walker  and  Appleyard  found  that  with  picric 
acid  and  silk  an  equilibrium  was  established  between 
the  fibre  and  solution  (dyeing  at  100°  C.). 

Also,  if  the  dyed  silk  was  treated  with  successive 
baths  of  water  the  action  was  reversible,  but  the 
time  taken  to  reach  a  state  of  equilibrium  was  much 
longer  (seven  hours).  It  did  not  matter  if  the  dye 
was  on  the  fibre  or  in  the  solution,  a  constant  ratio 
was  ultimately  obtained. 

The  result  does  not  necessarily  uphold  the  solid 
solution  theory.  It  is  equally  in  agreement  with 


PHYSICAL  ACTION  AND  SOLID  SOLUTION      177 

any  theory  which   requires  a  state  of  equilibrium, 
be  it  physical,  or  chemical. 

The  law  of  the  distribution  of  picric  acid  at 
60°  C.  was  found  to  be 

yw  =  35-5 

This  result  does  not  give  support  to  the  solid 
solution  theory,  for  it  indicates  that  the  molecule 
of  picric  acid  in  solution  is  2.7  times  as  great  as 
the  molecule  "  dissolved  "  in  the  silk. 

The  freezing-point  and  electrical  conductivity 
determinations  indicate  that  picric  acid  is  present 
in  water  in  a  simple  molecular  state.  Therefore,  so 
far  as  our  knowledge  goes,  it  is  impossible  to  recon- 
cile these  figures  with  any  theory  of  solid  solution. 

By  a  mathematical  transformation  of  the  above 
formula  we  obtain 

log  S  =  log  35.5  +  —  log  W. 

which  when  differentiated  becomes 

^S_  _i_    dW 
S  ~  2.7  '  W. 

This    indicates   that   if    the    concentration    in   the 
water  is  increased  by  any  volume,  the  concentration 

in  the  silk  will  increase  by  —  of  its  own  value. 

Formulae  of  this  nature  apply  in  many  cases  to 
absorption  phenomena.  Schmidt  and  Kiister  have 
shown  this  to  be  the  case  (Annalen,  283,  360). 

By  substituting  alcohol  for  water  in  these 
experiments,  in  which  picric  acid  is  more  soluble, 
less  was  taken  up  by  the  fibre.  The  ratio  of  the  two 

12 


178          CHEMISTRY  AND  PHYSICS  OF  DYEING 

concentrations  to  produce  the  same  shade  remains 
fairly  constant,  and  is  nearly  the  ratio  of  the  relative 
solubility  of  picric  acid  in  water  and  alcohol  at  60°  C. 

When  benzene  was  used  as  a  solvent,  abnormal 
results  were  obtained.  The  silk  would  not  take  up 
any  dye,  in  spite  of  the  fact  that  rosanilme  at  once 
colours  silk  from  this  solution.  Some  peculiarity 
in  the  system  is  indicated  here,  or  some  joint  property 
of  the  picric  acid  and  benzene  is  possibly  the  cause 
of  the  different  action.  The  difference  between  the 
dyeing  action  of  picric  acid  in  water,  and  benzene 
might  be  due  to  the  fact  that  in  the  former  it  is 
said  to  be  in  a  state  of  almost  complete  dissocia- 
tion, and  in  the  latter  it  is  scarcely  dissociated  at  all. 

In  this  case  it  would  be  the  H  ions  which  influ- 
ence dyeing,  as  sodium  picrate  will  not  dye  at  all. 
It  is  stated  also  that  picric  acid  dissociates  in 
alcohol. 

Benzoic  acid  is  readily  absorbed  by  silk.  A 
solution  of  this  acid  was  dissociated  to  the  extent 
of  6  per  cent.  The  salts  of  this  acid  are  also 
highly  dissociated,  and  any  addition  of  the  latter 
to  solutions  of  benzoic  acid  reduces  its  dissocia- 
tion from  6  per  cent,  to  zero.  It  would  be 
expected  that  a  smaller  percentage  of  acid  would 
be  absorbed  under  these  conditions.  The  absorp- 
tion is  actually  reduced  from  17  per  cent,  to  1.5 
per  cent.  The  reaction  does  not  hold  however  for 
alkaline  benzoates. 

Further  experiments  with  other  weak  acids  did 
not  corroborate  these  results.     No  relation  could  be 


PHYSICAL  ACTION  AND  SOLID  SOLUTION       179 

traced  between  the  relative  rate  of  dissociation  as 
measured  by  the  presence  of  H  ions  in  solution,  and 
the  relative  rate  of  absorption  by  silk.  If,  however, 
the  acids  be  divided  into  the  two  classes  of  aromatic 
and  fatty  acids,  a  much  closer  agreement  exists 
between  the  constants. 

The  average  absorption  of  the  aromatic  acids 
was  23  per  cent.,  that  of  the  fatty  acids  5  per  cent. 
In  most  cases  the  proportion  of  acid  absorbed 
to  acid  in  solution  bears  an  almost  constant  ratio, 
yet  in  some  cases  the  absorption  increases  rapidly 
as  the  acid  becomes  more  dilute.  With  citric  acid 
the  action  is  abnormal.  The  amount  taken  up  by 
the  silk  is  almost  independent  of  the  concentration, 
and  is  constant  in  amount. 

o  These  results  seem  to  indicate  that  a  solid 
solution  theory  is  unsatisfactory.  Solid  solution 
was  originally  defined  by  van't  Hoff  (Zeit.  Phys. 
Chem.  1890,  5,  322),  as  being  a  "  solid  homogeneous 
complex  of  several  substances,  the  proportions  of 
which  may  vary  without  affecting  the  homogeneity 
of  the  system. " 

Schneider  (Zeit.  Phys.  Chem.  1895,  10,  425) 
suggested  that  when  barium  sulphate  carried  down 
ferric  sulphate  from  its  solution,  the  action  was  of 
this  nature,  although  he  noticed  that  the  ferric  salt 
carried  down  was  proportional  to  the  amount  of 
the  insoluble  barium  compound  present,  up  to  the 
limits  of  occlusion.  Beyond  this  point  the  presence 
of  excess  of  iron  salt  in  the  solution  had  no  effect. 

More  recent  investigators  do  not  seem  to  agree 


i8o          CHEMISTRY  AND  PHYSICS  OF  DYEING 

with  this  suggestion.  Jannasch  and  Richards  (/. 
pr.  Chem.  1889,  39,  321)  consider  the  action  to  in 
some  way  involve  chemical  action,  rather  than  solid 
solution.  Ostwald  and  others  seem  to  agree  with 
this  view  of  the  case.  This  subject  received  further 
consideration  from  Hulett  and  Duschak  (Zeit.  Anorg. 
Chem.  1904,  40,  196),  who  have  further  noticed 
that  when  barium  chloride  is  absorbed  in  this  way 
by  barium  sulphate,  it  is  not  necessary  that  the 
soluble  salt  be  present  at  the  time  of  precipitation. 
When  finely  divided  crystals  of  the  sulphate  are 
suspended  in  the  solution  the  same  action  takes 
place.  They  further  consider  that  this  phenomenon 
may  be  due  to  the  formation  of  complex  salts,  such 
as  (BaCl2)SO4  or  (H.SO4)JBa. 

Quite  recently  Korte  (/.  Chem.  Soc.  1905,  1508), 
as  a  result  of  further  investigation  of  this  subject, 
does  not  agree  that  solid  solution  is  the  cause  of 
this  action. 

It  is  also  known  that  barium  sulphate  will  absorb 
metals  from  colloidal  solutions  of  the  same  (Vanino 
and  Hartl,  Ber.  1904,  37,  3620).  These  absorption 
results  with  such  a  comparatively  inert  substance 
as  barium  sulphate  will  give  the  dyer  an  insight 
into  the  possibility  of  some  such  action  taking 
part  in  the  phenomena  of  dyeing,  and  lake  formation. 

These  results  suggest  rather  that  "  absorption  " 
is  possible  under  such  conditions  as  are  indicated, 
and  that  this  is  by  no  means  confined  to  such 
conditions  as  approximate  to  those  which  obtain  in 
the  dye-house. 


CHAPTER  VIII 

EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING 

THE  suggestion  that  the  dyeing  action  is  primarily 
a  chemical  one,  has  received  support  in  the  past 
from  many  investigators  who  have  brought  forward 
evidence  in  favour  of  this  hypothesis. 

If  it  is  possible  to  prove  that  the  many  and 
varied  operations  in  dyeing  and  mordanting  are 
governed  by  the  laws  which  control  ordinary  chemical 
reactions,  it  is  evident  that  our  knowledge  of  the  sub- 
ject is  at  once  put  on  a  satisfactory  and  simple  basis. 

It  is,  therefore,  of  interest  to  follow  closely  the 
arguments,  and  facts,  which  have  been  recorded  in 
favour  of  this  view. 

Unfortunately,  the  conditions  under  which  much 
of  the  work  on  the  subject  has  been  effected  are 
not  entirely  satisfactory.  As  a  result,  some  of  the 
data  available  are  unreliable,  and  it  is  impossible 
to  allot  to  some  of  the  work  its  true  value  as 
evidence  in  favour  of  such  action. 

As  early  as  the  year  1737  Dufay  drew  attention  to 
the  possibility  of  the  dyeing  action  being  a  chemical 
one.  This  view  was  also  supported  by  Bergmann 
in  1776. 


182         CHEMISTRY  AND  PHYSICS  OF  DYEING 

In  these  early  days  the  relative  affinities  of 
different  fibres  for  the  same  dye-stuff  were  considered 
to  be  evidence  in  favour  of  chemical  action.  Berg- 
mann,  for  instance,  specially  pointed  out  that 
sulphate  of  indigo  is  attracted  by  wool  in  greater 
proportion  than  by  silk.  He  attributed  this  to 
the  greater  attraction  of  the  substance  of  the  former 
fibre  for  the  dye. 

Wool  was  said  to  exert  such  an  attraction  for 
the  dye  that  the  dye-bath  was  completely  ex- 
hausted. On  the  other  hand,  silk  could  only 
reduce  the  amount  present  in  the  dye-bath. 

From  this  it  is  evident  that  these  early  investiga- 
tors realised  this  factor  in  dyeing,  viz.,  the  attrac- 
tion of  the  fibre  for  the  dye ;  and  in  this  way  they 
differed  from  those  who  at  this  same  period 
ascribed  the  action  to  purely  mechanical  pheno- 
mena. If  it  can  be  established  that  dyeing  is 
primarily  due  to  this  cause,  the  subject  is  at  once 
narrowed  within  definite  limits. 

Macquer  in  1778,  in  his  "  Dictionnaire  de  Chimie," 
confirmed  the  idea  that  wool  and  all  animal  fibres  are 
the  materials  which  lend  themselves  most  readily 
to  the  dyeing  action.  He  stated  that  linen  and  all 
the  vegetable  fibres  are  the  most  difficult  to  dye, 
taking  the  least  number  of  dyes,  and  holding  them 
loosely.  He  placed  silk  in  an  intermediate  posi- 
tion, not  classifying  it  as  a  purely  animal  fibre.  He 
did  not  deny  that  this  variable  facility  of  taking 
and  retaining  different  substances  is  greatly  due 
to  the  number,  size,  and  arrangement  of  the  pores, 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     183 

and  their  relative  size  as  compared  with  the  dye 
particles,  but  he  did  not  allow  that  this  is  the  only 
cause  of  the  differences  experienced  in  dyeing  dif- 
ferent fibres,  and  of  the  results  obtained. 

In  support  of  this  statement  the  following  ex- 
perimental evidence  was  advanced.  If  one-pound  lots 
of  wool  and  silk  be  mordanted  with  alum  in  excess, 
and  dyed  separately  in  a  dye-bath  containing 
cochineal,  with  one  ounce  of  dye  in  each  case,  the 
wool  will  take  a  much  darker  colour.  To  obtain 
the  same  shade  on  the  silk  2\  ounces  of  colour  are 
necessary.  In  both  cases  the  dye-bath  is  exhausted. 
This  effectually  disposed  of  the  idea  put  forward  by 
d'Apligny  that  the  pores  are  smaller  in  the  case  of 
silk,  and  can  only  take  the  finest  particles  of  dye. 
Dyeing,  therefore,  is  not  simply  a  question  of 
encased  particles.  There  is  a  real  "  adherence  on 
contact,"  and  even  a  chemical  combination  varying 
with  the  properties  of  the  dyes  and  fibres  entering 
into  the  reaction.  He  was  of  opinion  that  the 
effect  of  a  surplus  number  of  pores  might  even 
diminish  the  colour-effect  by  concealing  the  coloured 
particles.  Dyeing  was  largely  a  question  of  surface 
action. 

Berthollet  in  his  "  Elements  of  Dyeing  "  collected 
all  the  facts  bearing  on  the  subject,  arid  favoured 
the  chemical  theory  as  a  result  of  his  investigations. 

Chevreul  also  came  to  the  conclusion  that  the 
action  of  dyeing  was  of  the  same  order  as  chemical 
action,  which  takes  place  slowly,  when  two  or  more 
bodies  are  in  contact. 


184          CHEMISTRY  AND  PHYSICS  OF  DYEING 

Persoz,  in  criticising  Crum's  mechanical  theory, 
held  that  the  view  that  acetate  of  alumina  is  de- 
composed naturally  by  the  cotton  fibre,  just  in 
the  same  way  as  it  would  be  if  the  fibre  were 
absent,  is  untenable.  He  refused  to  believe  that 
the  same  amount  of  alumina  would  be  given  up  by 
the  acetate  in  contact  with  mica  plates.  This 
difference  would  be  still  more  marked  at  an  elevated 
temperature.  He  therefore  considered  that  the 
cotton  fibre  exerted  a  powerful  influence  on  the 
decomposition  of  the  aluminium  salt.  (See  p.  143.) 

He  actually  gave  particulars  showing,  in  the 
case  of  alum  solution,  that  actual  decomposition 
of  the  solution  took  place  when  cotton  or  silk  was 
in  contact  with  it.  He  recorded  that  the  solution 
became  more  acid,  owing  to  its  being  deprived  of 
a  notable  amount  of  its  base. 

These  experiments  are  probably  the  first  of  a 
series  dealing  with  the  decomposition  of  salts  in 
solution  by  fibres.  They  may  be  regarded  as  the 
first  direct  indication  that  the  action  might  be  a 
chemical  one.  Macquer's  results  might  have  been 
due  to  mechanical,  or  even  optical  causes,  but  this 
experiment  stands  on  a  different  basis,  and  the 
proof  of  chemical  action  was  thought  to  be  a  con- 
vincing one. 

These  results  do  not  agree  with  Crum's  con- 
tention that  the  rate  of  change  in  a  solution  of 
acetate  of  alumina  is  the  same  whether  a  fibre  be 
present  or  not.  Persoz  also  asked  how  the  colour 
mixed  with  so  viscous  a  solution  as  gum  or  starch 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     185 

can  occupy  these  sacs  expelling  the  air  and  taking 
its  place  in  the  printing  of  fabrics. 

He  stated  also  that  a  fibre  impregnated  with 
manganese  dioxide  should  not  dye,  yet  it  is  in  a 
very  favourable  state  to  take  up  indigo.  The  fact 
that  some  substances,  such  as  baryta,  calcium 
sulphate,  &c.,  are  never  fixed  by  the  fibre,  while 
others  are,  is,  he  claimed,  in  favour  of  the  chemical 
theory. 

Muspratt  ("  Chemistry  as  applied  to  Arts,"  p. 
766)  thought  that  compounds  deposited  on  wool 
or  cotton  became  fixed  through  different  causes. 
"  Wool  is  strongly  contracted  by  acids,  and  it  is 
only  under  their  influence  that  we  can  fix  colours 
upon  it.  Cotton  is  contracted  by  alkali,  a  colour 
adheres  to  it  only  in  so  far  as  it  presents  an  alkaline 
reaction."  The  idea  was  also"  advanced  that  the 
different  colours  assumed  by  wool,  silk,  and  cotton 
with  the  same  dye,  were  due  to  configuration  of  the 
fibres. 

Kuhlmann  (Compt.  Rend.,  April  1856)  dyed 
samples  of  cotton  and  linen  which  had  been  nitrated, 
and  noted  the  results  obtained.  The  pyroxylin  was 
well  washed  with  water,  and  ultimately  with  soda. 
After  mordanting  and  "  ageing,"  samples  of  these 
materials  were  dyed.  All  the  nitrated  fibres  gave 
excessively  pale  shades,  as  compared  with  the 
natural  fibres.  There  seemed  to  be  evidence  that 
although  the  treated  fibres  rejected  the  mordants,  yet 
they  had  increased  attraction  for  the  madder  itself. 
Similar  results  were  obtained  with  Prussian  blue. 


186          CHEMISTRY  AND  PHYSICS  OF  DYEING 

To  obviate  the  possibility  of  these  results  being 
due  to  physical  alteration  in  the  fibre,  he  used 
Bechamp's  process  to  denitrate  the  fibre,  and  noted 
that  the  cotton  immediately  recovered  its  property 
of  receiving  mordants  and  colours.  The  effect  of 
varying  the  degree  of  nitration  was  to  give  varying 
results.  He  extended  those  experiments  to  wool, 
silk,  hair,  &c. 

It  was  also  noticed  that  picric  acid  gave  a  very 
strong  tint  on  nitrated  cotton. 

Kuhlmann  concluded  that  the  chemical  com- 
position of  the  bodies  to  be  dyed  had  the  greatest 
influence  upon  the  dyeing;  also  that  dyeing  is  due 
to  chemical  combination,  and  that  the  effects  due 
to  capillarity,  and  the  peculiar  structure  of  the 
material,  were  of  secondary  importance. 

It  may  be  pointed  out  that  the  early  authorities 
who  favoured  a  chemical  theory,  based  their  theo- 
retical conclusions  on  the  hypothesis  that  the  dyeing 
action  was  similar  to,  say,  the  reaction  between 
caustic  soda  and  hydrochloric  acid.  In  other  words, 
that  it  was  a  definite,  and  simple  one. 

It  is  assumed  to-day  by  those  who  favour  chemi- 
cal action,  that  the  animal  fibres  possess  acid  and 
basic  properties.  They  therefore  combine  with 
and  fix  the  dye-stuff,  at  least  those  which  possess 
either  acidic  or  basic  properties  themselves.  We 
may  therefore  get  actual  salt  formation. 

The  fact  that  the  animal  fibres  contain  amido- 
acids  is  therefore  the  basis  of  this  theory.  The  fibre 
substance  therefore  contains  both  amido  and 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     187 

hydroxyl  groups,  which  play  their  part  in  the  respec- 
tive cases  where  basic  and  acid  dyes  are  used. 

These  two  species  of  dyes  might  even  be  dyed 
on  a  fibre  already  mordanted  and  dyed  with  alizarine 
the  lake  of  which  would  be  held  mechanically.  The 
mordant  in  this  case  would  also  be  attracted  chemi- 
cally, and  then  by  double  decomposition,  or  otherwise 
the  lake  would  be  formed. 

The  statement  has  been  made  that  "  there  is  no 
colouring-matter  which  does  not  possess  either  acid 
or  basic  properties"  ("Manual  of  Dyeing,"  page  8). 

The  first  time  that  the  idea  was  put  forward 
that  wool  plays  the  part  of  an  acid  in  the  dyeing 
of  basic  dyes  (magenta)  was  in  1884  (J.S.D.  and 
C.  i,  209),  when  Hummel  likened  the  action  of 
the  fibre  to  the  fixing  action  for  dyes  of  oleic,  or 
tannic  acid  on  cotton,  &c.  Although  Hummel  did 
not  state  in  terms  the  decomposition  which  must 
take  place  when  a  basic  hydrochloride  combined 
with  the  wool  substance  in  this  way,  yet  it  is 
clear  that  the  hydrochloride  must  split  up  in  order 
to  enable  the  base  to  combine  with  the  acid. 

In  the  case  of  wool  it  was  afterwards  pointed  out 
by  Knecht  (J.S.D.  and  C.  1888,  page  72),  that  when 
this  fibre  is  dyed  with  basic  dyes  (hydrochloride), 
that  the  whole  of  their  acid  is  left  in  the  solution. 

If  the  amido  theory  is  correct,  it  is  difficult  to 
explain  why  the  acid  does  not  combine  with  the 
fibre.  The  writer  doubts  if  the  same  result  would 
be  found^  with  silk  when  the  affinity  of  that  fibre 
for  acids  is  considered. 


188 


CHEMISTRY  AND  PHYSICS  OF  DYEING 


Hummel  also  claims  that  this  action  is  visible 
to  the  eye.  When  a  colourless  rosaniline  salt  is  used, 
the  fibre  is  coloured  magenta. 

It  is  claimed  ("Manual  of  Dyeing/'  p.  8)  that 
this  conclusively  proves  the  chemical  theory,  and 
that  a  coloured  salt  is  formed  with  one  of  the  con- 
stituents of  the  fibre. 

If  the  action  is  a  chemical  one,  it  will  follow 
that  a  point  will  be  reached  when  the  fibre  sub- 
stance will  all  be  used  up,  and  a  point  of  maximum 
absorption  attained.  The  following  experiments 
are  put  forward  by  Knecht  and  Appleyard  (f.S.D. 
and  C.  1889,  p.  74),  to  prove  that  this  is  the  case. 
Silk  was  dyed  with  a  large  excess  of  picric  acid  and 
naphthol  yellow  respectively,  with  the  following 
results. 


Picric  acid. 

Naph.Yel.S 

Tartrazine. 

Amount  fixed    . 
Do.  in  solution 

13.2% 

37  o% 

20.8% 
29.2% 

22.65% 
27-35% 

Fifty  per  cent,  of  dye  was  taken  in  each  case  on 
the  weight  of  the  fibre  dyed.  The  ratio  taken  up 
of  Naphthol  Yellow  to  picric  acid  20.8/13.2  is  in  the 
ratio  of  their  molecular  weights. 

Tartrazine  does  not  seem  to  follow  this  law, 
however.  As  picric  acid  contains  one  OH  group, 
Naphthol  Yellow  one  OH  and  one  SO3Na,  and 
tartrazine  2CO.OH  and  2SO3Na  groups,  it  is 
difficult  to  decide  in  what  way  they  might,  or 
might  not,  combine  with  the  fibre  substance. 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     189 

Von  Prager  and  Ulrichs  (Farb.  Zeit.  1891,  373) 
hold  that  these  results  are  unreliable,  and  v. 
Georgievics  denies  that  the  Naphthol  Yellow  and 
picric  acid  are  taken  up  in  molecular  proportions. 

Recently  (J.S.D.  and  C.  1904,  p.  242),  Knecht 
has  brought  forward  results  which  he  contends  add 
support  the  chemical  theory. 

By  an  improved  method  of  analysis  and  work- 
ing with  pure  dyes,  the  following  absorption  results 
were  obtained : 


Dye  used. 

Amt.  used. 

Taken  up. 

Calculated. 

Orange  G. 

50% 

16.24% 

Crystal  Scarlet 

50% 

18.23% 

18.02% 

Scarlet  2  G.  . 

50% 

16.37% 

Xylidine  Scarlet 

50% 

17.12% 

J7-30% 

Orange  G. 

25% 

15.68% 

Crystal  Scarlet 

25% 

1742% 

*74°% 

Scarlet  2  G.  . 

25% 

15.53% 

Xylidine  Scarlet 

25% 

16.22% 

16.40% 

Orange  G.,  Atomic  wt.  452,  Crystal  Scarlet  502, 
Scarlet  2G.  452,   Xylidine  Scarlet  479. 

Picric  acid  is  now  said  to  act  in  an  abnormal 
way,  and  not  in  the  way  originally  stated.  In 
dyeing  wool  with  increasing  amounts  of  dye-stuff, 
a  limit  of  absorption  is  reached  in  each  case. 

For  instance,  with  Crystal  Scarlet  the  following 
results  were  obtained  : 


Percentage  of  colour  used  : 

50        25        22.5     20        17.5     15       12.5 
Percentage  of  colour  taken  up  by  fibre  : 

18.2     17.3     17.0     16.6     15.3     14.2     11.9 


10     7.5     5.0     2.5 

9.6      7.2      4.7      2.2 


I9o          CHEMISTRY  AND  PHYSICS  OF  DYEING 

This  author  holds  that  these  experiments  favour 
a  chemical  theory,  from  the  fact  that  the  dyes  are 
taken  up  in  molecular  proportions. 

The  effect  of  excess  of  acid  in  dyeing  is  said  to 
be  due  to  the  production  of  degraded  products  in 
the  fibre,  which  resemble  lanuginic  acid  in  their 
chemical  action. 

The  fact  that  the  water  can  be  varied,  within 
limits,  without  altering  the  percentage  of  dye  taken 
up  is  held  to  disprove  the  solid  solution  theory.  If 
this  is  so,  and  with  such  a  definite  chemical  action 
as  is  claimed,  the  fact  that  up  to  the  point  of  satura- 
tion the  dye  is  not  all  removed  from  the  liquid 
would  seem  equally  to  point  against  a  chemical 
action  on  the  old  hard  and  fast  lines. 

The  law  of  mass  action  might  possibly  influence 
the  result  however. 

Alizarine  S.  (powder),  oxalic  acid  and  alum  can 
be  boiled  together  indefinitely  without  combination 
or  at  any  rate,  any  visible  change.  If  lanuginic 
acid,  said  to  be  present  in  wool,  is  added,  a  bright 
scarlet  precipitate  is  formed.  This  is  said  to  give 
additional  evidence  in  favour  of  the  chemical  view. 

As  before  pointed  out  the  above  ratio  breaks 
down  entirely  in  the  case  of  the  sulphonic  acids  of 
phenols  and  amines.  Dehydrothiotoluidinesulphonic 
acid  is  readily  absorbed  by  silk,  yet  Prof.  Green 
could  not  find  any  of  the  above  which  had  an 
affinity  for  the  animal  or  vegetable  fibres.  It  is 
very  difficult  to  explain  why  these  sulphonic  acids 
are  not  attracted  by  the  animal  fibres.  The  amido 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     191 

acid  theory  requires  that  they  shall  be  readily 
absorbed.  If  the  animal  fibres  have  in  their  sub- 
stance a  compound  which  readily  combines  with 
acid  compounds,  the  only  explanation  of  the  above 
is  that  soluble  compounds  are  formed. 

In  the  case  of  wool  very  little  dyeing  action 
takes  place  in  a  simple  solution  of  these  dyes  in 
water.  No  figures  are  available  for  silk.  If,  how- 
ever, an  acid  be  added  to  the  solution  the  colour 
acid  is  set  free,  and  rapidly  dyes  the  fibre,  in  the 
case  of  silk  at  ordinary  temperatures. 

A  preliminary  treatment  of  wool  with  sulphuric 
acid,  followed  by  very  thorough  washing,  will  cause 
this  fibre  to  dye  rapidly,  when  introduced  into  a 
neutral  solution  of  an  acid  dye  in  the  form  of  its 
sodium  salt. 

It  is  claimed  that  this  can  be  satisfactorily 
explained  by  assuming  that  the  wool  fibre  has  affinity 
for  the  acid,  and  retains  sufficient  to  set  free  the 
colour  acid.  It  would  seem,  however,  that  this 
explanation  is  not  altogether  satisfactory. 

An  addition  of  sulphuric  acid  over  and  above 
that  necessary  to  decompose  the  dye  acid  salt  has 
an  altogether  abnormal  effect  on  the  rate  of  dyeing. 
If  the  dyeing  action  is  a  strictly  chemical  one,  the 
excess  of  sulphuric  acid  might  be  expected  to  have 
the  opposite  effect.  The  nature  of  this  reaction 
is  well  illustrated  by  the  following  experiment. 
Boiling  in  distilled  water  will  partly  remove 
the  dye  (colour  acid)  from  a  silk  skein.  If  then 
a  few  drops  of  a  strong  acid  are  added  to  the 


192          CHEMISTRY  AND  PHYSICS  OF  DYEING 

solution  nearly  all  the  colour  will  return  on  to  the 
fibre. 

It  is  difficult  to  understand  this  action  from 
the  chemical  point  of  veiw.  In  what  form  is 
the  re-dissolved  colour  in  the  solution  ?  If  present 
as  free  acid,  why  should  the  addition  of  acid  influence 
the  result  ?  If,  on  the  other  hand,  the  colour  acid 
fibre  compound  is  not  decomposed,  but  dissolves 
out  in  the  hot  water,  can  the  conditions  exist  under 
which  this  fibre  compound  is  decomposed  on  the 
addition  of  acid,  the  colour  acid  set  free,  and  the 
latter  combine  to  form  the  same  compound  in  the 
fibre  again  in  the  presence  of  the  acid  which  has 
decomposed  it  in  the  solution  ?  The  opposite 
effect  might  be  expected,  viz.,  that  the  sulphuric 
acid  would  partly  replace  the  colour  acid.  This 
matter  seems  to  deserve  special  attention. 

It  is  contended  that  the  substances  in  the 
animal  fibres  which  produce  these  dye  lakes  or 
compounds  can  be  isolated. 

Prof.  Liechti  states  that  albumin  will  decompose 
a  basic  dye  in  much  the  same  way  as  an  animal 
fibre.  In  this  case  also,  the  acid  remains  in  the 
solution.  It  will  be  remembered,  however,  as 
mentioned  elsewhere,  that  this  decomposing  action 
is  not  confined  to  organic  compounds  of  animal 
origin,  but  may  take  place  with  such  inert  substances 
as  porcelain.  It  is  claimed  for  the  above  reaction 
that  "  here  there  can  be  no  doubt  that  chemical 
combination  takes  place,  as  the  coagulated  albumin 
is  dyed  magenta. " 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     193 

The  proof  here  is  not  more  satisfactory  than  it 
is  in  the  case  of  magenta-dyed  wool.  In  order  to 
uphold  such  a  statement  it  is  necessary  to  ignore 
the  general  reactions  obtained  with  substances  of 
the  above  nature. 

Knecht  states  that  if  wool,  or  silk,  be  dyed  with 
night  blue,  and  the  dye  subsequently  extracted 
with  alcohol,  the  compound  actually  formed  between 
the  dye  and  the  fibre  is  extracted.  If  this  solution 
be  treated  with  barium  hydroxide,  the  night  blue  is 
precipitated,  and  the  fibre  substance  can  be  recog- 
nised in  the  solution. 

This  has  been  denied  (Zeii.  fur  Farb.  und  Text. 
Ch.  1903,  215),  it  being  maintained  that  no  such 
action  will  take  place  if  the  wool  is  purified  with 
alcohol  before  dyeing.  The  organic  matter  extracted 
is  not  of  the  nature  stated,  but  consists  of  substances 
extracted  by  alcohol  alone. 

This  criticism  has  been  answered  (f.S.D.  and  C. 
1904,  72),  by  Knecht  repeating  his  experiments  after 
a  preliminary  treatment  with  alcohol.  Under  these 
conditions  he  states  that  he  obtained  a  yellow 
residue,  smelling  of  burning  wool  after  ignition,  and 
precipitated  by  an  aqueous  solution  of  night  blue, 
or  magenta.  It  would  have  been  more  satisfactory 
if  a  blank  experiment  had  been  .  made  side  by  side 
with  the  night  blue  one,  in  addition  to  the  pre- 
liminary purification. 

At  first  sight  the  case  for  the  chemical  theory 
seems  to  receive  support  from  the  action  of  nitrous 
acid  on  the  fibre,  and  subsequent  development  with 

13 


194         CHEMISTRY  AND  PHYSICS  OF  DYEING 

phenols,  &c.  There  does  not  seem  to  be  any  doubt 
as  to  the  action  in  this  case.  The  silk  shows  by  its 
altered  colour  that  the  nitrous  acid  has  acted  on  it 
and  the  subsequent  development  with  phenols,  or 
amines,  is  rapid  and  startling  in  its  nature.  It 
is  certainly  the  case  that  some  constituent  of 
the  fibre  actually  enters  into  the  reaction,  which 
produces  these  "dyes."  An  attempt  made  by  the 
writer  to  isolate  these  compounds  was  not  very 
successful.  They  seemed  to  be  present  in  very 
small  quantities. 

No  other  experiments  seem  to  afford  such  a  clear 
indication  that  chemical  action  may  take  place  in 
the  process  of  dyeing.  It  might  be  fairly  argued 
that  the  dyeing  action  is  of  a  strictly  chemical 
nature,  if  the  matter  rested  here. 

Unfortunately,  these  experiments  and  their  influ- 
ence on  the  action  of  dyeing  have  been  discounted 
by  some  experiments  of  Bentz  and  Farrell  (J. S.C.I. 
16,  405).  After  confirming  the  above  reactions,  and 
that  silk  contains  amido  groups,  the  fibre  was 
treated  with  nitrous  acid  for  thirteen  hours.  After 
washing  the  fibre  was  boiled  with  alcohol,  or  an 
acid  solution  of  cuprous  chloride.  This  removed  the 
amido  groups.  The  fibre  would  not  then  rediazotise. 
The  NH2  (or  NH)  groups  had  been  removed.  From 
the  chemical  point  of  view  it  is,  therefore,  clear  that 
the  fibre  should  not  dye  under  these  conditions. 
But  the  "  deamidated"  fibre  takes  acid  colours 
equally  as  well  as  the  original  fibre.  Therefore, 
the  inference  is  drawn  that  the  amido  groups  play 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     195 

little  or  no  part  in  the  dyeing  of  silk  (or  wool) 
with  acid  colours. 

These  experiments  need  to  be  extended  ;  they 
should  cover  the  subsequent  resistance  against  soap, 
water,  and  alcohol.  This  should  show  if  the  amido 
groups  play  any  secondary  part  by  holding  the  dye 
when  it  is  once  on  the  fibre. 

The  writer  (J.S.C.I.  13,  96)  gave  the  results  of 
a  number  of  experiments  on  dyes  dyed  direct 
and  ingrain  respectively.  Figures  are  given,  show- 
ing by  curves  and  tables  the  differences  obtained  by 
dyeing  primuline  colours  "  direct  "  and  "  ingrain  " 
on  silk. 

Their  fastness  against  soap  and  alkali  solutions 
at  a  high  temperature,  was  taken  as  a  compara- 
tive measure  of  the  way  the  dyes  are  held  by  the 
fibre.  A  standard  solution  of  neutral  soap,  or 
sodium  carbonate  was  used  in  all  cases. 

The  general  results  obtained  were  as  follows  : 

The  difference  in  fastness  of  the  dyes  when  dyed 
"  ingrain  "  and  direct  was  very  noticeable.  This  is 
clearly  shown  in  the  series  of  curves  accompanying 
the  paper. 

The  dyes  when  dyed  direct  were  not  so  fast  as 
the  original  primuline  against  soap  solution. 

The  developed  amine  dyes  are,  with  one  excep- 
tion, very  much  faster  in  their  resistance  to  soap 
than  the  corresponding  alcoholic  or  phenolic  dyes. 
It  may  be  argued  from  this,  either  that  the  fibroin 
shows  a  stronger  acid  than  basic  reaction,  as  mea- 
sured in  this  way,  or  that  the  solvent  action  of 


196         CHEMISTRY  AND   PHYSICS   OF   DYEING 

the  soap  is  greater  in  the  case  of  the  alcoholic  dyes 
than  in  the  other.  Either  of  these  explanations  is 
possible. 

It  will  be  noticed  that  in  the  one  case  given  of 
an  azo  triple  dye,  that  the  resistance  against  soap 
is  increased  in  the  ratio  of  1.7  to  i.  This  may,  again, 
be  due  to  increased  molecular  volume,  or  to  a 
state  of  greater  insolubility.  It  would  have  been 
interesting  to  have  used  a  phenol  in  the  case  of 
the  second  development,  and  also  to  have  dyed  the 
azo  dye  direct,  and  noted  the  effect  of  one  or  two 
developments  on  the  fastness  against  soap.  The 
only  possible  comparison  given  is  that  of  Atlas  Red 
R  developed  with  /3-naphthol.  This  dye  is  prepared 
by  diazotising  primuline,  and  combining  with 
w-tolylenediamine . 

This  dye  was  not  so  fast  as  might  be  reasonably 
expected.  It  was  argued  from  these  figures  that 
the  relative  fastness  of  these  two  classes  of  developed 
dyes  was  not  so  much  due  to  internal  molecular 
structure  as  to  the  phenolic,  or  basic  nature  of  the 
dye. 

Some  "  developers  "  will  not  act  on  the  diazo- 
tised  primuline  on  silk.  /3-naphtholsulphonic  acid 
(R  salt)  is  an  example.  This  can  hardly  be  due 
to  a  simple  matter  of  diffusion  of  the  developers, 
for  substances  (dissolved)  which  are  present  in  the 
ratio  of  their  molecular  weights,  exert  equal 
pressure  at  the  same  temperatures. 

If  this  is  so,  it  should  be  easily  confirmed  by 
nothing  the  relative  amount  of  the  " developers" 


EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     197 

absorbed  by  equivalent  solutions.  An  alternate 
suggestion  is  that  the  diazotised  primuline  has 
an  affinity  for  this  silk  fibre  which  the  R  salt  cannot 
overcome.  The  presence  of  a  sulphonic  acid  group 
in  the  developer  may  influence  the  reaction,  and 
also  the  solution  state  of  the  developer. 

The  fact  remains,  at  any  rate,  that  the  R  salt 
is  unable  to  combine  with  the  diazotised  primuline 
in  a  silk  fibre,  but  able  to  do  so  in  a  cotton  one. 

The  relative  rate  of  development  with  R  salt 
on  cotton  and  mercerised  cotton  where  the  fibre 
is  in  a  higher  state  of  hydration  might  throw 
further  light  on  this  subject. 

The  relative  amounts  of  dye  taken  up  under 
standard  conditions  from  soap  solution  do  not  seem 
however,  to  indicate  that  the  fibre  has  much  chemi- 
cal influence  on  the  amount  of  dye  absorbed  by 
the  dye,  as  the  following  table  taken  from  my  paper 
(ibid.)  will  show. 

D  Per  cent,  of  dye  taken 

up  by  fibre. 

Primuline  and  C,,H5.OH    .         »  0.18 

„       C6H5NH2   .         .  0.19 

„       C6H4(NH2)2         |  o.n 

„      /3C]0H7.OH      ^f  0.12 

„      C6H4.COOH.OH  o.n 

The  table  on  p.  198  shows  the  result  obtained 
in  the  experiments  by  boiling  for  different  times  in 
standard  soap  solution,  and  covers  most  of  the 
developers  used  in  practice. 

The  samples  of  silk  were  dyed  with  the  equiva- 
lent quantities  of  the  dyes,  or  equivalent  propor- 


198         CHEMISTRY  AND  PHYSICS  OF  DYEING 


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EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING     199 

tions  of  primuline.  The  conditions  of  dyeing  were 
kept  constant  in  all  cases.  After  drying  the 
sample  lots  of  silk  were  boiled  out  for  the  periods 
indicated,  and  the  resulting  shades  were  carefully 
compared  with  standard  samples ;  or  else  the  dye 
in  the  soap  solution  was  estimated  by  colorimetric 
methods.  In  this  way,  the  loss  of  colour  on  boil- 
ing off  was  estimated  with  a  sufficient  degree  of 
accuracy. 

The  ratio  of  colour  removed  in  the  case  of  these 


Dye. 

Developer. 

"In- 
grain" x. 

"Direct" 

y- 

X 

y 

Remarks. 

Primuline 

C6H5.OH 

0.20 

0.74 

i 

- 

C6H4(OH)2(i.3) 

0.17 

0.75 

i 

" 

C6H4.OH.COOH(i.2) 

0.  12 

0.75 

i 

6^2" 

" 

C10H7.OH/3       . 

0.15 

0.63 

i 

4.2 

'• 

NH4.OH 

0.08 

0.50 

i 
^ 

" 

C6H5.NH2         . 

O.  IO 

0.70 

i 

Azo  dye. 

" 

C6H5.NH2 

0.05 

0.61 

\ 

I2.O 

Azo  triple  dye. 

» 

C6H5.NH2         . 

0.07 

0.32 

I 

4T6 

Na2CO3 

" 

C6H4.(NH2)2(i.3)        . 

0.052 

0.80 

i 
15.4 

" 

C10H7.NH2/3     . 

0.27 

0.79 

i 

" 

C10H7.OH/3      . 

0-27 

0.76 

I 

200         CHEMISTRY   AND   PHYSICS   OF  DYEING 

dyes  is  seen  in  the  table  on  p.  199.  The  influence 
of  the  solvent  (soap,  or  sodium  carbonate)  seems  to 
alter  the  rate  of  "boiling  out"  materially. 

It  is  very  difficult  to  reconcile  these  results  with 
any  purely  chemical,  or  solid  solution,  theory.  The 
stumbling-block  is  the  altered  fastness  of  dyes  dyed 
ingrain  and  direct,  and  the  indication  that  the  dyes 
may  be  fixed  in  two  ways.  The  difference  between 
the  fastness  of  the  phenolic  and  amine  dyes  respec- 
tively may  be  explained  in  other  ways. 

The  affinity  of  these  dyes  from  primuline  for 
cotton  seems  to  vary  greatly,  and  here  again  the 
metaphenylenedi amine  colour  has  a  fair  affinity 
for  this  fibre,  and  the  beta-naphthol  one  very  little. 
These  results  are  obtained  when  dyeing  this  fibre 
direct.  It  is  therefore  quite  clear  that  a  difference 
in  dyeing  properties  is  apparent  when  amines  are 
used  in  place  of  phenols  in  the  production  of  these 
dyes. 

Another  point  of  importance  was  indicated.  It 
was  shown  that  the  colours  produced  in  the  two 
cases,  direct  and  ingrain,  were  not  identical  in  shade, 
as  shown  in  the  table  on  p.  201. 

This  might  indicate  some  difference  either  in  the 
action  or  state  of  the  dye.  This  has  since  been 
suggested  by  Brand  (Proc.  Soc.  Ind.  de  Mulh.,  Feb. 
and  April  1901)  as  being  due  to  a  secondary  action 
between  the  diazo  compounds  and  the  wool.  In 
my  paper  I  indicated  that  the  fact  that  some 
developers  wrould  not  act  on  the  diazotised  primu- 
line might  be  taken  as  a  possible  proof  that  there 


EVIDENCE  OF  CHEMICAL  ACTION    IN   DYEING     201 

was  some  action  between  the  diazo  compound  and 
the  fibre.  The  same  explanation  has  more  recently 
been  put  forward  by  Hepburn  (J.S.D.  and  C.  1901, 
279). 

Taking  the  case  of  para-nitraniline,  the  fastness 
of  the  dye  against  washing  is  said  by  Brand  to  be 
due  to  the  paranitrodiazobenzene  being  partially 
reduced  at  the  expense  of  the  fibre  substance  to 


Dye. 

Developer. 

Colour  obtained. 

Method  of 
dyeing. 

Primuline 

CCH,OH      .     . 

Yellow. 

Ingrain. 

5  J                                   •               • 

Do.,  slightly  darker. 

Direct. 

C(iH3.NH2     .      . 

Yellow  (brown  shade). 

Ingrain. 

?  j             • 

Do.,  slightly  darker. 

Direct. 

C6H4(OH)2i.3     . 

Orange. 

Ingrain. 

Do.,  redder  shade. 

Direct. 

Ct;H4(NH)2i.3    ! 

Red-brown. 

Ingrain. 

5  1                                            • 

Do.,  redder  shade. 

Direct. 

C,H4.OH.COOH 

Yellow. 

Ingram. 

5? 

Do.,  slightly  duller. 

Direct. 

para-nitraniline.  The  excess  of  diazo  compound 
would  react,  forming  dinitrodiazoamidobenzene. 
This  substance  is  very  insoluble. 

It  is  just  possible  that  a  similar  reaction  may 
take  place  in  the  case  of  diazotised  primuline,  and 
that  it  is  this  compound  which  is  so  sensitive  to 
light,  but  it  is  not  so  easy  to  explain  the  subsequent 
action  of  the  developers. 

It  is  held  by  Rossi  (Rev.  Gen.  Chem.  1901,  670) 
that  silk  will  also  act  on  diazo  compounds  as  a 
reducing  agent,  diazoamido  or  azoamido  compounds 


202         CHEMISTRY  AND   PHYSICS   OF  DYEING 

being  formed,  the  difference  being  determined  by 
the  stability  of  the  diazoamido  compounds.  This 
reaction  once  ended,  the  resulting  compounds  are 
held  mechanically  by  the  fibre. 

The   reduced   action   of   some   developers   may, 


Resistance  of  Phenolic  dyes  to  the  action  of  soap.     (Dreaper.) 


10  20  30  40  50  6omins. 

Time  of  boiling  out.    - 

FASTNESS    OF    INGRAIN    COLOURS. 

A  :  C6H5.OH  (ingrain).   B  ;  do.  (direct).    C :  C10Hr.OH/3  (ingrain). 
D  :  do  (direct).     E  :  Primuline  (direct). 

however,  be  due  either  to  the  diazo  compounds 
being  held  by  the  fibres  by  some  secondary  chemi- 
cal action,  or  else  to  the  molecular  aggregates  of 
these  developers  being  too  large  to  enter  the  fibre 
substance  in  the  form  in  which  they  are  present 
in  the  solution. 


EVIDENCE  OF  CHEMICAL  ACTION   IN   DYEING    203 

If  some  such  reducing  action  takes  place  as  is 
indicated  when  these  dyes  are  developed  in  silk,  what 
is  the  corresponding  action  in  the  case  of  cotton  ? 

The  curves  drawn  from  the    above  tables  (see 

Resistance  of  Amine  dyes  to  the  action  of  soap.     (Dreaper.) 


10  20  30  40  50  6omins. 

Time  of  boiling  out. 

FASTNESS    OF    INGRAIN    COLOURS. 

A  :C6H5.NH2  (ingrain).   B  :  do.  (direct).   C :  C10H7.NH2/3  (ingrain). 
D;  do.  (direct).     E:  Primuline  (direct). 

p.  202)  will  also  illustrate  the  relative  resistance  of 
the  phenolic  dyes  towards  the  action  of  the  standard 
soap  solution.  They  show  the  general  results  which 
may  be  expected  in  practice,  and  the  relative  fast- 
ness of  the  dyes. 

The  extra  fastness   of  the  ingrain   dye  in  the 
case  of,  say,  cotton   fibre   and   the   phenolic  dyes 


204        CHEMISTRY  AND  PHYSICS  OF  DYEING 

after  a  treatment  with  soda  is  certainly  difficult  to 
understand,  from  a  purely  physical  point  of  view. 
Mineral  colours,  however,  which  are  "  developed  " 
or  formed  on  the  fibre  are  certainly  more  resistant 
to  the  action  of  such  solutions,  and  it  is  not  likely 
that  anything  more  than  a  modification  in  the 
physical  state  of  the  precipitate,  and  its  position 
in  the  fibre,  are  the  cause  of  this  extra  fastness  over 
that  of  the  same  mineral  colours  applied  direct. 

In  the  same  way,  the  similar  curves  obtained 
from  the  corresponding  amines  are  recorded  (see 
p.  203).  It  will  be  noticed  that  in  this  case  the 
amine  with  the  higher  molecular  weight  is  the  less 
resistant  to  the  action  of  the  soap  liquor. 

In  this  respect  it  differs  from  the  corresponding 
phenol.  No  general  law  can  be  given,  as  it  is 
known  that  the  resorcinol  dye  is  not  so  fast  as 
either  the  phenol  or  naphthol  compounds. 

Pauly  and  Binz  (Zeit.  /.  Farb.  Text.  Chem.  1904, 
373)  consider  that  the  dyeing  property  of  silk  and 
wool  is  due  to  the  tyrosine  present  in  albuminoid 
combination,  and  that  it  reacts  by  virtue  of  its 
phenolic  character.  Pure  tyrosine  gives  similar  re- 
sults, but  some  albuminoids  like  salmine  and  scorn- 
brine,  do  not  react  in  this  way.  Silk  reacts  (dyes) 
better  than  wool,  because  it  has  more  tyrosine  in 
its  composition  in  the  ratio  of  10  per  cent,  to 

3-3i  Per  cent- 

It  is  not  clear,  however,  that  silk  does  dye  better 

than  wool.  It  is  generally  acknowledged  that  the 
reverse  is  the  case.  Silk  may  dye  more  readily,  it 


EVIDENCE  OF  CHEMICAL  ACTION   IN   DYEING     205 

is  true,  but  these  authors  do  not  attempt  to  show 
that  a  standard  dye  will  be  taken  up  in  the  ratio 
of  10  to  3. 5  at  the  saturation-point  by  the  two  fibres, 
which  should  follow  if  this  theory  is  correct. 

The  presence  of  tyrosine  in  the  silk  fibre  is 
indicated  as  follows.  This  fibre  gives  on  oxidation  an 
indophenol  or  oxazine  reaction  in  a  similar  way  to 
that  obtained  with  a  mixture  of  a  />-diamine  and 
a  phenol. 

If  silk  be  soaked  in  a  .05  per  cent,  solution  of 
dimethyl  />-phenylenediamine  in  the  presence  of 
acetic  acid  and  sodium  acetate,  and  bromine  water 
added,  the  silk  fibre  takes  a  slate  grey  colour.  In 
the  absence  of  silk  (or  wool)  no  such  colour  is  pro- 
duced. This  reaction  takes  place  with  tyrosine 
itself. 

1.4  amidonaphthol  will  react  in  the  same  way. 
Erdmann's  patented  process  for  dyeing  feathers, 
&c.,  is  based  on  this  reaction. 

Some  evidence  brought  forward  by  Knecht 
(J.S.D.  and  C.  1902,  p.  103)  complicates,  and  in 
a  way  tends  to  disprove  the  amido-acid  theory. 

The  substances  he  isolated  from  wool  and  silk 
dyed  with  night  blue  would  only  combine  with 
basic  dyes,  and  not  with  acid  ones.  He  also  separ- 
rated  a  compound  from  silk  which  was  stated  to 
combine  only  with  acid  dyes. 

The  results  obtained  up  to  the  present  time  by 
different  investigators  may  be  summed  up  as  follows. 

Colours  may  be  obtained  by  treating  silk  and 
wool  with  nitrous  acid,  and  phenols  or  amines, 


206         CHEMISTRY  AND   PHYSICS  OF   DYEING 

Therefore,  silk  or  wool  may  be  dyed  in  this  way. 
Deamidated  fibres  can  be  dyed  as  well  as  the  original 
ones,  so  that  the  dyeing  property  of  silk  or  wool  is 
not  necessarily  due  to  NH  or  NH.2  groups. 

The  relative  action  of  the  diamine  colours  on 
animal  and  vegetable  fibres  is  difficult  to  under- 
stand, when  considered  from  the  chemical  point 
of  view.  For  instance,  cotton  may  be  dyed  black, 
and  wool  be  left  white  on  dyeing  in  the  cold  with 
Diamine  Black,  BWH. 

In  a  paper  on  the  "  Chemistry  of  Wool/*  M. 
Matthews  (/.  Franklin,  Inst.  CLIX.,  No.  5,  397) 
favours  the  amido-acid  theory  for  the  following 
reasons : 

(1)  NH3  is  among  the  products  of  destrutcive 
distillation  of  wool. 

(2)  Wool  is  easily  hydrolised  by  dilute  alkaline 
solutions. 

(3)  It   readily   combines   with   acids,   and   even 
with  boiling  dilute  sulphuric  acid. 

(4)  The  nitrous  acid  reaction. 

(5)  The  well-defined  basic  properties  of  the  fibre. 
The  following  so-called  "  coefficients  of  acidity  " 

are  given: 

Wool       ...       57 

Silk         .         .         .     143 

Albumin  .          .       20.9 

Gelatin    .          .          .       28.4 

All  these  facts  may  be  readily  allowed,  but  the 
evidence  of  the  chemical  nature  of  dyeing  must 
ultimately  rest  on  a  more  direct  foundation,  in  view 
of  the  conflicting  nature  of  the  evidence,  when  it  is 


EVIDENCE  OF   CHEMICAL  ACTION  IN  DYEING     207 

considered  from  a  general  point  of  view,  and  is 
taken  in  conjunction  with  other  recorded  facts. 

Even  if  the  substantive  colours  owe  their  attri- 
butes to  the  grouping>N  -  R  -  N<as  held  by  Vignon, 
this  theory  is  not  applicable  to  many  colours  like 
primuline,  the  mono-azo  dyes,  &c.,  as  pointed  out 
by  Green  and  Levy  (J.S.D.  and  C.  13,  1898). 

As  far  back  as  1886  Mohlau  attributed  the  sub- 
stantive qualities  to  the  alleged  fact  that  benzidine 
could  be  extracted  from  its  solutions  by  bleached 
cotton. 

The  above  authors  show  that  no  affinity  exists 
between  benzidine  and  the  cotton  fibre,  or  even 
mercerised  cotton.  Dianisidine  hydrochloride  gave 
the  same  negative  results. 

It  is  considered  by  Willstatter  (Ber.  1904,  3758) 
that  if  the  dyeing  of  wool  is  due  to  salt  formation, 
the  fibre  as  an  optically  active  substance  should 
be  capable  of  transforming,  or  "  splitting,"  a  racemic 
dye-stuff  into  its  optically  active  constituents. 

No  racemic  dye-stuff  being  available,  the  hydro- 
chlorides  of  atropine  and  homatropine  were  used 
in  the  experiments. 

An  examination  of  the  alkaloids  left  in  the  bath 
still  showed  that  they  were  in  no  way  changed,  and 
remained  optically  inactive. 

The  inference  is  that  no  salt  formation  takes 
place. 


CHAPTER  IX. 

EVIDENCE  OF  CHEMICAL  ACTION  IN  DYEING 

(continued) 

THE  suggestion  that  dyeing  is  primarily  due  to 
chemical  action  rather  than  physical  action  has  re- 
ceived the  support  of  R.  Hirsch  (Chem.Zeit.  13,  432). 

He  assumed  that  "  Knecht  has  established  be- 
yond doubt /that  dyeing  of  animal  fibres  is  a  chemical 
process. " 

Such  being  the  case  there  is  no  reason  why  dyes 
alone  should  be  regarded  as  capable  of  absorption 
unless  these  compounds  have  something  in  common 
from  a  chemical  point  of  view,  which  distinguishes 
them  from  other  compounds.  Nietzki  has  endea- 
voured to  show  that  this  is  the  case  (Chem.  d.  org. 
Farbst.,  2nd  ed.). 

The  difficulty  in  including  the  nitro  bodies  in  such 
a  scheme  is  evident.  Nietzki  meets  this  objection 
with  the  statement  that  nitrophenols  have  most 
probably  a  similar  constitution  to  the  nitrosophenols, 
which  are  now  generally  regarded  as  quinone  oximes. 

Hirsch  does  not,  however,  agree  with  this  view. 
Experiments  were  made  to  ascertain  if  wool  has  any 
affinity  for  organic  substances  in  general. 


EVIDENCE  OF  CHEMICAL  ACTION   IN  DYEING     209 

If  wool  is  "  dyed "  with  /3-naphtholsulphonic 
acid  R,  the  greater  part  of  the  sulphonic  acid  is 
absorbed,  and  resists  the  action  of  boiling  water; 
when  the  wool  is  put  into  a  solution  containing  diazo- 
benzene,  or  diazoxylene,  the  corresponding  colour  is 
developed  with  ease. 

The  nature  of  the  alkali  added  to  the  bath 
greatly  influenced  the  rapidity  of  the  development. 
With  sodium  carbonate  the  action  was  very  slow. 
Similar  results  were  obtained  by  producing  Naphthol 
Green  (Cassella)on  the  fibre.  Naphthionic  acid  was 
fixed  on  wool  in  either  acid  or  alkaline  solutions. 

On  the  other  hand,  sulphanilic  acid  combined 
with  great  difficulty  with  wool. 

G.  H.  Hirst's  statement  that  a  benzidine  sulphate 
solution  boiled  with  silk,  or  cotton,  contains  all  its 
sulphuric  acid  at  the  end  of  the  experiment,  is  no 
proof  that  the  benzidine  is  taken  up  by  the  fibre. 

These  experiments  seem  to  indicate  that  wool 
will  absorb  organic  substances  of  the  nature  of 
naphtholsulphonic  acids,  and  that  an  acid  state  of 
the  solution  is  more  favourable  for  absorption  than 
an  alkaline  one. 

The  fact  that  naphthionic  acid  is  fixed  by  the 
wool  in  both  acid  and  alkaline  solutions  is  probably 
against  <a  chemical  theory.  Sulphanilic  acid  (p.- 
amidobenzenesulphonic  acid)  is  absorbed  with  great 
difficulty,  and  only  in  concentrated  solutions. 

Three  years  later,  Binz  and  Schroeter  (Ber.  1902, 
p.  4225)  supported  the  chemical  theory,  but  they  did 
not  admit  that  in  all  cases  the  fixation  of  substantive 

14 


210          CHEMISTRY  AND  PHYSICS  OF  DYEING 

dyes  is  due  to  salt  formation  between  dye-stuff  and 
fibre. 

The  fact  that  certain  acid  dyes  will  dye  wool  and 
silk  in  the  presence  of  either  acid,  or  alkali  (caustic 
alkali),  and  that  there  are  basic  dyes  which  will  dye 
in  strongly  acid  solutions,  is  against  any  simple  theory 
of  salt  formation.  It  is  clear  that  some  other  action 
is  involved. 

Azobenzene-w.w'-disulphonic  acid  and  p.-a.zo- 
benzenemonosulphonic  acid  will  both  dye  wool  in 
an  acid  bath.  The  "  colours"  will  stand  washing 
with  water,  but  are  instantly  discharged  by  dilute 
sodium  hydrate  solution.  These  examples  therefore 
conform  to  a  salt  producing  theory.  If,  however, 
we  dye  with  />.-hydroxyazobenzene  we  get  an  intense 
yellow  in  acid,  neutral,  or  alkaline  solutions.  Salt 
formation  is  therefore  unlikely  in  this  case. 

Again,  />.-amidoazobenzene  and  p.  -dimethyl 
amidoazobenzene  dye  wool  an  intense  yellow  in  a 
solution  containing  a  small  proportion  of  acid.  The 
same  shade  is  obtained,  however,  if  the  proportion 
of  acid  is  increased  to  6,  12,  20,  or  even  120  molecules 
of  acid  to  each  molecule  of  dye. 

Further  experiments  showed  that  the  hydro- 
chlorides  of  w.w'-diamidoazobenzene  and  tetra- 
methyl-w.w'-diamidoazobenzene  gave  different  re- 
sults. After  an  addition  of  6  to  10  molecules  of 
hydrochloric  acid  to  each  molecule  of  base  the  wool 
remained  quite  white. 

The  following  conclusions  were  drawn  from  the 
experiments.  The  groups  NH2  and  N(CH3)2  in 


EVIDENCE  OF  CHEMICAL  ACTION   IN   DYEING    211 

the  meta-position  to  the  azo  groups,  and  the  pre- 
sence of  the  sulphonic  acid  groups  impart  to  the 
chromogen  dyeing  properties  which  result  in  the 
formation  of  loose  salts  with  the  animal  fibres. 

A  different  state  of  affairs  is  assumed  in  the  case 
where  the  OH,  NH2,  or  N(CH3)2  groups  are  in  the 
para-position.  In  the  latter  case  the  dyeing  pro- 
perties cannot  be  overcome  by  the  addition  of  alkali 
to  solutions  of  the  phenDlic  dye-stuff,  or  of  acid  to 
the  basic  substances. 

Most  of  the  substantive  dyes  for  wool  and  silk 
contain  the  amido-  and  hydroxyl-groups  in  the  ortho- 
and  para-positions  relatively  to  the  chromophor, 
and  can  be  regarded  as  giving  quinone  derivatives 
as  isodynamic  forms.  When,  however,  these  groups 
are  present  in  the  meta-position,  quinone  formation 
does  not  occur,  and  the  dyeing  is  only  a  question  of 
salt  formation,  and  that  of  a  loose  nature. 

In  the  other  cases  where  true  dyeing  is  said  to 
take  place,  the  action  is  probably  due  to  a  condensa- 
tion in  the  nucleus  between  the  dye-stuff  and  the  fibre. 

In  answer  to  a  severe  criticism  by  v.  Georgievics, 
which  is  noticed  elsewhere,  in  which  the  conditions 
of  the  experiments  are  attacked,  Binz  and  Schroeter 
they  bring  further  evidence  in  support  of  their  case 
(Ber.  1903,  3008). 

Azobenzenecarboxylic  acid  is  a  dye-stuff  in  the 
same  sense  as  the  corresponding  sulphonic  acid, 
but  it  will  dye  only  in  neutral  solution. 

Again,  />-.benzeneazo-trimethylammonium  hy- 
droxide dyes  wool,  but  the  colour  is  destroyed  by  the 


212         CHEMISTRY  AND  PHYSICS  OF  DYEING 

addition  of  hydrochloric  acid  in  equivalent  quantity 
to  the  dye-stuff  fixed. 

The  fact  that  chrysoidine  and  Bismarck  brown 
give  darker  shades  in  the  presence  of  hydrochloric 
acid  is  noted  in  confirmation  of  the  idea  that  p.- 
amidoazobenzene  yields  with  the  fibre  a  condensation 
product,  and  not  a  salt.  It  is  therefore  contended 
that  azobenzenesulphonic  acid  and  carboxylic  acids, 
m-amidoazobenzenes  and  quaternary  ammonium 
bases  of  the  azo  compounds  dye  with  simple  salt 
formation. 

On  the  other  hand,  ortho-  and  para-amido- 
azobenzenes  and  most  of  the  ortho-  and  p.- 
hydroxyazo  compounds  cannot  give  normal  salts. 

Here  a  condensation  of  the  fibre  substance  with 
the  quinoid  nucleus  of  the  dye-stuff  is  said  to  take 
place. 

These  experiments  will  require  extending  before 
such  definite  statements  can  be  accepted.  For 
instance,  they  do  not  agree  with  Prof.  Green's  results 
obtained  with  the  sulphonic  acids. 

These  authors  still  further  defend  themselves 
against  a  second  criticism  by  v.  Georgievics  (Ber. 
1904,  727).  They  deny  that  the  neutral  sodium 
salt  of  azobenzene-/>. -sulphonic  acid  is  capable  of 
dyeing  wool  in  neutral  solution.  They  claim  that 
the  wool  used  must  have  contained  free  sulphuric 
acid. 

They  also  consider  that  the  fact  that  alcohol 
will  remove  the  dyes  from  the  fibre  is  not  proof  that 
there  is  no  combination  between  the  dye  and  fibre. 


EVIDENCE   OF   CHEMICAL  ACTION   IN   DYEING     213 

The  solvent  action  may  be  due  to  decomposition 
of  the  fibre  dye  compounds  first  formed. 

They  do  not  seem  to  meet  the  statement  that 
benzene  will  act  in  the  same  way.  They  also  deny 
that  picric  acid  is  extracted  by  alcohol  from  wool 
after  dyeing. 

Many  of  the  contradictory  results  obtained  by 
different  observers  may  be  due  to  the  different  con- 
ditions of  dyeing,  fibre  state,  &c. 

Hirsch's  experiments  might  well  be  compared 
with  the  above  in  their  general  effect. 

Examining  the  tinctorial  values  of  the  three 
isomeric  hydroxyazobenzenes  (Zeit.  /.  Farb.  und 
Text.  Ind.  1904,  p.  177),  Prager  criticises  the  results 
obtained  by  Binz  and  Schroeter.  He  will  not  allow 
that  dyeing  may  be  a  condensation  in  the  nucleus 
between  the  quinoid  dye-stuff,  and  the  substance 
of  the  fibre. 

The  ortho-  and  para-hydroxyazobenzenes  are 
capable  of  assuming  the  quinone  type,  but  the 
meta-compound  cannot  apparently  assume  an 
isodynamic  form.  The  meta-compound  should 
therefore  not  act  as  a  dye. 

In  practice  it  is  found  that  the  meta-compound 
will  dye  wool,  as  well  as  the  para-compound.  These 
results  are  held  not  to  favour  the  condensation 
theory. 

Collecting  some  of  the  facts  recorded  in  this 
chapter  and  elsewhere,  the  conflicting  nature  of  the 
evidence  in  favour  of  a  simple  chemical  theory  will 
be  at  once  realised. 


214         CHEMISTRY  AND  PHYSICS  OF  DYEING 

1884.  Miiller  Jacobs.  Amido-azobenzene  will 
not  dye  cotton,  di-  and  triamidobenzenes  will  do  so. 

1889.  Ewer  and  Pick.  Naphthylenediamines. 
Position  of  amido  groups  determines  dyeing  power 
on  cotton  (QI  a3  positive  dyes). 

1889.  Hirsch.  /3-Naphtholsulphonic  acid  R. 
dyes  wool.  Naphthionic  acid  fixed  by  wool  (acid 
or  alkaline).  Sulphanilic  acid  has  very  slight 
affinity  for  wool. 

1894.  Green.  Colourless  sulphonic  acids  have 
no  affinity  for  animal  or  vegetable  fibres.  Dehydro- 
thiotoluidinesulphonic  acid  an  exception  in  the  case 
of  animal  fibres. 

Colour  derived  from  metaphenylenediamine  and 
primuline  will  dye  cotton,  that  from  /3-naphthol 
will  not. 

1902.  Binz  and  Schroeter.     Azobenzene  m.m'- 
disulphonic  acid  and    />.-azobenzenesulphonic   acid 
dye  wool  from  an  acid  bath  ;   />.-oxy-azobenzene  dyes 
wool  in  acid,  neutral,  or  alkali   bath,  />.-amidoazo- 
benzene    and    />.-dimethylamidoazobenzene   dye  in 
acid  bath  of  any  strength. 

Hydrochlorides  of  w.w'-diamidoazobenzene  and 
tetramethyl-w.w'-diamidoazobenzene,  dye  wool  in 
neutral  solution,  but  not  acid. 

1903.  Binz    and  Schroeter.       Azobenzenecarb- 
oxylic    acid   and  ^.-benzeneazotrimethylammonium 
hydroxide  will  dye  in  neutral  baths,  but  not  in  acid. 

1904.  Prager.  o.-  w.-and  />.-bydroxyazobenzenes 
dye  wool  in  acid  solutions. 

1904.     Binz  and  Schroeter.     The  sodium  salt  of 


EVIDENCE  OF  CHEMICAL   ACTION   IN   DYEING    215 

azobenzene  ^.-sulphonic  acid  is  not  capable  of  dyeing 
wool. 

It  will  be  at  once  seen  that  the  reactions  which 
take  place  in  dyeing  are,  from  a  chemical  point  of 
view,  of  such  a  nature  that  it  is  difficult  to  appreciate 
their  true  value. 

It  is  not  easy  to  explain  the  action  of  some  dye 
solvents  on  dyed  mixtures  of  cotton  and  silk.  It 
is  well  known  that  some  dyes  may  be  dissolved  out 
of  the  silk  fibre  and  not  taken  out  of  the  cotton  by 
a  solution  of  ammonium  acetate.  In  this  way 
"  shot  "  effects  may  be  produced. 

It  is  generally  agreed  that  cotton  is  comparatively 
inert  as  an  absorbent  of  dyes,  yet  under  these  con- 
ditions we  have  an  enormously  increased  attraction 
as  compared  with  silk.  With  these  dyes  we  may 
even  obtain  black  cotton  and  white  silk. 

A  further  study  of  the  relative  "  absorption  " 
of  the  dyes  in  the  respective  fibres  under  varying 
conditions  may  clear  up  this  point,  and  will  be 
considered. 

In  the  year  1884  Bcettinger  discovered  a  dye 
which  he  named  Congo  Red.  He  found  that  it 
possessed  the  then  extraordinary  property  of  dyeing 
cotton  direct  from  aqueous  solution  as  well  as  it 
dyed  silk. 

The  whole  subject  of  the  action  of  these  direct 
dyes  on  cotton  (and  other  fibres)  is  little  understood. 

In  a  general  way,  there  seems  to  be  some  connec- 
tion between  the  constitution  of  the  dye  molecule 
and  its  action.  It  seems  to  be  important  that  the 


216         CHEMISTRY  AND  PHYSICS  OF  DYEING 

amido-groups  occupy  the  para-position,  and  that 
the  ortho-positions  be  occupied  by  a  hydrogen 
radical.  The  meta-position  seems  to  have  little 
influence  in  the  dyeing  or  tinctorial  properties. 

The    double    chromophorous    group  ~N^NI^  in 

the  tetrazo  dyes  seems  to  influence  the  dyeing  in 
some  way,  but  the  presence  of  this  group  alone  does 
not  suffice  to  make  the  dye  a  "  direct  "  one. 

The  primuline  dyes  do  not  contain  this  group, 
nor  are  they  azo  dyes  at  all. 

They  possess  the  chromophorous  group  <^>c- 

Some  dyes  contain  both  this  and  an  azo  group ;  a 
dye  of  this  nature  is  Cotton  Yellow  R. 

It  may  be  said  here  that  the  view  of  chemical 
action  occurring  in  the  dyeing  of  these  colours  is 
unsatisfactory  so  far  as  the  dyeing  of  cotton  is  con- 
cerned. In  fact,  the  advent  of  these  dyes  has 
been  as  unexpected,  and  revolutionary,  from  the 
theoretical  as  from  the  practical  point  of  view. 

The  fact  remains  that  there  are  many  dyes  which 
dye  cotton  direct  under  conditions  which  seem  to 
exclude  any  chemical  action. 

In  certain  cases,  the  affinity  of  the  cotton  for 
the  dye  is  so  great  that  the  bath  is  almost  exhausted. 
This  is  so  in  the  case  of  Diamine  Fast  Red  F.  In 
other  cases  a  great  proportion  of  the  dye  is  left  in 
the  solution.  The  facts  known  about  the  dyeing 
of  these  dyes  are  incomplete.  The  dye  in  most 
cases  is  readily  removed  by  water.  This  is,  of  course, 
noticed  with  other  dyes  on  silk.  The  amount  of 


EVIDENCE   OF  CHEMICAL  ACTION   IN   DYEING     217 

dye  taken  up  seems  to  vary  with  the  concentration 
but  no  careful  work  has  been  done  on  this  subject. 
The  results  could  not  fail  to  be  interesting.  The 
addition  of  neutral  salts  and  their  great  effect  on 
the  rate  of  dyeing  in  solutions  containing  these 
substances  is  very  instructive.  Their  action  from 
a  chemical  point  of  view  is  difficult  to  gauge.  The 
fact  that  these  dyes  are  less  soluble  in  the  salt  solu- 
tions possibly  accounts  for  their  action,  and  this 
fact  seems  to  point  to  a  physical  rather  than  a 
chemical  process.  The  fact  also  that  these  dyes  will, 
when  on  the  fibre,  combine  with  or  form  lakes  with 
the  basic  dyes  seems  to  show  that  the  dyes  are  not 
in  combination  with  the  fibre  (Knecht,  J.C.D.  and 
C.  1886,  2). 

The  attraction  of  these  dyes  for  wool  and  silk 
is  also  a  strong  one,  as  is  seen  when  the  test  of 
resistance  is  applied  to  the  action  of  the  ordinary 
solvents  (water,  &c.). 

The  factor  which  operates  in  the  case  of  cotton 
therefore  seems  to  have  a  similar  value  in  the  dyeing 
of  silk  or  wool. 

A  point  which  must  be  noticed  is,  that  these 
dyes  seem  on  the  animal  fibres  to  have  a  greater 
resistance  to  the  action  of  light  than  the  same 
colours  on  cotton. 

It  seems  strange,  also,  that  these  dyes  are  taken 
up  more  readily  in  alkaline  solutions  by  cotton,  and 
more  readily  in  acid  solutions  by  silk. 

Diamine  Milling  Black  is  even  said  to  dye 
well  in  a  solution  containing  7  ozs.  of  soap  and 


2i8          CHEMISTRY  AND  PHYSICS  OF  DYEING 

ij  ozs.  of  soda  to  a  gallon  (Text.  Manuf.  1901,  p. 

3I9). 

In  the  practical  dyeing  of  cotton  three  supple- 
mentary processes  are  used  to  increase  the  fastness 
of  these  dyes,  viz.,  diazotising ;  treatment  with 
metallic  salts;  or  the  "coupling"  process.  From 
their  action  it  will  be  necessary  to  briefly  describe 
them  here. 

Diazotising  produces  shades  which  are  very 
resistant  to  the  action  of  soap  solutions  at  the  boil, 
and  sometimes  to  light. 

After  dyeing,  the  fibre  is  put  through  a  solution 
of  nitrous  acid,  subsequently  washed,  and  "  devel- 
oped "  in  solutions  of  amines,  or  phenols. 

In  practice  /3-naphthol,  m.-phenylenediamine 
or  resorcinol  are  chiefly  used  as  developers. 

In  the  case  of  primuline,  chloride  of  lime  gives 
a  very  fast  yellow  if  it  follows  the  diazotising  process. 

The  increased  fastness  produced  by  the  treat- 
ment with  metallic  salts  is  also  noticeable. 

The  shades  are  faster  against  the  action  of  soap 
and  light. 

Treatment  with  copper  sulphate,  although  it 
does  not  act  so  universally  as  was  at  first  claimed, 
gives  very  satisfactory  results  in  many  cases. 

Diamine  Sky  Blue  F.F.  is  greatly  increased  in 
fastness.  Diamine  Brill.  Blue  G.  is  claimed  to  give 
as  fast  colours  as  vat  indigo  blue  in  this  way. 

At  one  time  it  was  thought  that  treatment  with 
copper  sulphate  would  increase  the  fastness  of  all 
dyes. 


EVIDENCE  OF  CHEMICAL  ACTION   IN   DYEING     219 

Bichromate  of  potash  gives  greater  fastness 
against  soaping  with  Diamine  Jet  Black  and  Diamine 
Brown  M. 

Fluoride  of  chrome  is  also  used  with  Diamine 
Bronze,  Fast  Red  F.,  &c.,  to  produce  the  same  effect. 
Where  the  action  is  not  that  of  a  mordant  it  is  obscure. 

The  process  known  as  coupling  has  been  already 
referred  to.  Here  basic  dyes  are  added  to  the  bath 
and  fixed  by  direct  combination,  or  lake  formation. 

The  difficulty  attending  the  production  of  a 
satisfactory  theory  to  explain  the  varied  results 
obtained  in  the  dyeing  of  cotton  has  been  increased 
by  the  addition  of  still  another  class  of  dyes,  viz., 
the  sulphur  dyes ;  it  would,  perhaps,  be  more 
correct  to  say  by  the  extension  of  this  class,  for 
Cachou  de  Laval  may  be  considered  a  member  of 
this  group. 

These  colours  are  produced  by  soaking  the  cotton 
fibre  in  a  hot  alkaline  bath  in  the  presence  of  sul- 
phide of  sodium. 

The  colours  are  developed  and  fixed  by  subse- 
quent exposure  to  the  air  (oxidation). 

The  extra  fastness  of  dyes  produced  in  the  fibre 
is  generally  noticeable. 

In  this  case  the  dye  is  soluble  in  the  alkaline 
bath  by  reduction,  and  subsequently  by  oxidation 
insoluble  dyes  are  produced  in  the  fibre  itself.  In 
some  cases  a  more  energetic  oxidation  is  necessary. 
Immedial  Blue  C.  may  be  developed  by  hydrogen- 
peroxide  or  by  the  combined  action  of  steam  and 
alkali. 


220          CHEMISTRY  AND  PHYSICS  OF  DYEING 

Until  we  know  more  about  the  constitution  of 
these  dyes  it  is  only  possible  to  speculate  as  to  the 
exact  nature  of  their  development. 

In  the  dyeing  of  indigo,  also,  some  similar  action 
plays  at  least  a  secondary  part.  Indigo  is  present 
in  the  dye  vat  in  a  soluble  and  reduced  form. 
Subsequent  oxidation  of  the  indigo  white  after 
absorption  in  the  fibre  produces  the  insoluble  indigo 
in  situ.  The  dye  so  formed  is  remarkably  fast 
against  the  action  of  light,  or  soap  solution.  It 
may,  however,  "  rub  "  badly  if  the  operation  of 
developing  is  improperly  conducted. 

So  far  as  we  know  we  can  reproduce  the  condi- 
tions of  formation  of  these  "  oxidation  "  dyes  as 
they  exist  in  the  presence  of  a  fibre.  There  is  no 
reason  to  think  that  the  formation  of  the  insoluble 
dye-substances  in  the  fibre  material  takes  a  different 
course  to  that  taken  in  solution,  in  the  above  cases. 

The  action  of  tannic  acid  on  organic  colloids  is 
an  instructive  one.  The  tanning  of  leather  is  of 
such  a  nature,  that  the  theoretical  work  connected 
with  tanning  should  be  closely  followed  by  those 
interested  in  the  general  operations  of  dyeing. 

The  nature  of  the  attraction  which  silk  exhibits 
for  tannic  acid  is  indicated  as  follows.  It  is  more 
readily  removed  from  the  fibre  by  a  dilute  solution 
of  hydrochloric  acid  than  by  a  solution  of  sodium 
carbonate. 

The  reaction  between  oxy cellulose  and  basic  dyes 
has  been  studied  by  Vignon  (Compt.  Rend.  125,  448). 

It   is   found  that   this  substance  has   a  greater 


EVIDENCE   OF   CHEMICAL   ACTION   IN   DYEING     221 

attraction  for  these  dyes  than  the  unaltered  cellu- 
lose. This  will  be  seen  in  the  following  table,  which 
gives  the  results  obtained  with  one  gramme  of  fibre. 

Fibre,  Safranine,  Methylene  blue, 

Cellulose  .  .  .000  g.  absorbed  .002  g.  absorbed 
Oxycellulose  .  .007  g.  ,,  .006  g.  ,, 

The  same  investigator  (Compt.  Rend.  1887,  125, 
357)  has  made  an  attempt  to  determine  the  mole- 
cular groups  which  confer  on  certain  dyes  the  property 
of  dyeing  cotton  direct.  Compounds  having  similar 
constitutions  to  these  dyes  were  taken.  The  basic 
substances  were  employed  in  the  form  of  their  hydro- 
chlorides,  and  their  action  in  the  presence  of  cotton 
carefully  noted. 

The  following  table  shows  the  relative  absorp- 
tion of  a  number  of  organic  substances. 

Substances  absorbed  by  cotton,  Neutral  bath,     Alkaline  bath, 

Ammonia           ....  .2--4  . .           .2 

Hydroxylamine           .          .          .  .o-.3  . .           .2 

Hydrazine          .          .          .          .  1.2  ..         1.7 

Phenylhydrazine         .          .          .  3.6  . .          2.9 

Aniline      .....  .1  .1 

Dimethylaniline          ...  .o  .o 

Diphenylamine  ....  .4  .4 

o.-Phenylenediamine            .          .  .4  .6 

m  -Phenylenediamine           .          .  6.4  . .         2.4 

/>.-Phenylenediamine            .          .  6.7  3.2 

Benzidine           .          .          .          .  6.0  ..         5.6 

Tetramethylbenzidine          .          .  7.0  6.3 

Benzidinesulphonic  acid      .          .  7.4  . .         4.8 

Diamidostilbenedisulphonic  acid .  3.5  ..         3.6 

Dianisidine         ....  6.Q  . .          5.7 

Diamidonaphthalene  .          .          .  i.o  1.7 

The  following  conclusions  are  drawn  by  Vignon 


222          CHEMISTRY  AND  PHYSICS  OF  DYEING 

from  the  results  recorded  in  this  table.  Fixation 
is  held  to  be  due  to  chemical  action  depending  on 
molecular  grouping.  The  dyeing  is  not  due  to  the 
benzene  nucleus  containing  free  nitrogen  atoms,  or 
two  nitrogen  atoms  joined  together  to  form  azo- 
groups,  since  diphenyl,  ammonia,  hydroxylamine,  and 
azobenzene  are  not  absorbed.  The  diamines,  with  the 
exception  of  o.-phenylenediamine  and  the  hydrazines 
are  absorbed  to  a  considerable  extent,  and  the 
absorption  appears  to  be  independent  of  the  degree 
of  saturation  of  the  azotised  molecular  groups. 

It  is  argued  from  these  results  that  the  dyeing 
property  seems  to  be  due  to  the  grouping 

>N— R— N<  or  >N— N< 

that  is  to  say  to  the  hydrazine  N  atoms  united 
directly,  or  indirectly  by  means  of  aromatic  residues. 
It  is  further  argued  that  in  the  case  of  the  direct 
colouring-matters  the  nitrogen  atoms  unite  with  the 
cellulose  molecule  and  then  become  pentatonic. 

>N-N< 

A    A 

The  fact  that  benzidine  and  tetramethylene- 
benzidine  are  absorbed  by  cotton,  whereas  the  methyl 
iodide  compound  of  the  latter  in  which  the  nitrogen 
atoms  are  already  pentatonic  is  not  taken  up,  also 
lends  support  to  this  theory. 

The  thermo-chemical  investigations  of  Vignon 
are  instructive  (Bull.  Soc.  Chim.  1890,  3,  405  and 
Compt.  Rend,  no,  p.  909),  and  are  held  by  that 
investigator  to  support  a  chemical  theory.  Dealing 


EVIDENCE  OF  CHEMICAL  ACTION   IN  DYEING     223 

first  with  silk  in  the  "  raw  "  and  "  boiled  off  "  state, 
the  following  results  ware  obtained : 


Raw  Silk, 

Boiled-off  Silk, 

Reagents  N/i  sols. 

Calc.  for 

Cal.formolJ  Calc.  for 

Calc.  for 

100  grms. 

wt.  in  grms. 

100  grms. 

mol.  wt. 

Water      . 

.10 

3-5 

-15 

5-2 

Pot.  Hydrate  . 

i-35 

47.0 

1.30 

45-25 

Sod.  Hydrate  . 

i-55 

53-95 

1.30 

45-25 

Ammonia 

•65 

22.65 

•50 

I7-4 

H2S04      . 

•95 

33-iQ 

.90 

31-35 

HC1 

•95 

33-10 

.90 

31-35 

HNO2      . 

.90 

31-35 

•85 

29.60 

KC1 

.20 

6-95 

.10 

3-50 

6.65 

6.00 

The  above  figures  represent  the  heat-units 
evolved,  the  average  temperature  of  the  experiments 
being  12°  C.  The  formula  for  gum  silk  was  taken 
as  C141H232N48O56,  and  that  of  the  boiled  off  silk  as 
the  same. 

The  alkalies  removed  some  of  the  silk  gum.  The 
total  number  of  heat-units  evolved  was  6.0  in  the 
case  of  ungummed  silk,  and  6.65  in  the  case  of  the 
raw  silk. 

The  results  obtained  in  the  case  of  wool  were 
different. 


Reagent  N/i  sol. 

KHO 

NaHO       . 
HC1 
H,S04        . 


Heat-units  per 
i  oo  grms. 

1.16 


•95 
•99 


Heat-uuits  for 


24.50 
24.30 
20.05 
20.90 


224        CHEMISTRY  AND  PHYSICS  OF  DYEING 

These  experiments  were  made  on  unbleached 
woollen  thread. 

Turning  to  cotton  it  was  noticed  that  the  rise  in 
temperature  took  seven  or  eight  minutes  to  reach 
its  maximum.  The  following  results  were  obtained  : 

Reagents.  Cotton  thread  unbleached.        Cotton  wool  bleached. 


per  100  grms. 

C6H1005. 

per  100  grms. 

C6H1005. 

KHO     . 

.80 

1-3 

-  .  .  •      1.4        .  . 

2.27 

NaHO    . 

.         .65 

1.05 

1-35     ,  - 

2.  2O 

HC1 

.40 

•65 

.40     .. 

.65 

H2S04    . 

.         .38 

.60 

..         .36     .. 

.58 

The  effect  of  bleaching  on  the  thermo-chemical 
reactions  in  the  case  of  cotton  is  important.  Vignon 
considers  that  the  difference  is  due  to  the  presence 
of  oxycellulose  in  the  latter. 

These  results  would  in  themselves  indicate  that  a 
chemical  reaction  may  take  place  under  the  recorded 
conditions.  It  has,  however,  been  shown  (Goppels- 
roeder,  Centr.  /.  Text.  Ind.,  No.  38)  that  both 
indigo  and  Turkey  Red  are  attracted  with  greater 
avidity  by  oxycellulose  and  chlorocellulose,  but 
there  does  not  seem  to  be  much  evidence  that  chemi- 
cal action  can  take  place  in  the  dyeing  of  these 
colours. 

Furthermore  (Chem.  Zeit.  23,  1891),  Vignon  ex- 
perimented with  the  object  of  increasing  the  activity 
of  cellulose  fibre  by  chemical  means.  Treatment 
with  ammonia  at  100° — 200°  C  resulted  in  the  fibre 
taking  up  nitrogen.  The  result  in  the  calorimeter 
with  this  product  indicated  that  the  fibre  was  more 


EVIDENCE  OF  CHEMICAL  ACTION   IN  DYEING     225 

basic.  This  treated  fibre  will  attract  large  quantities 
of  acid  dyes  giving  dark  shades. 

The  influence  of  this  treatment  seems  to  be  very 
great,  and  the  attraction  for  dyes  is  increased. 

Experiments  with  stannic  and  metastannic  acids 
also  give  important  results  when  they  are  "  dyed  " 
with  phenosafranine. 

Stannic  acid  absorbed  63  per  cent,  of  the  dye  in 
a  standard  solution. 

Metastannic  acid  absorbed  o  per  cent,  of  the  dye 
in  a  standard  solution.  The  more  strongly  acid 
oxide  fixes  the  most  colour. 

Vignon  sums  up  the  results  of  his  experiments 
(Chem.  Zeit.  10, 1891),  and  considers  that  the  following 
facts  are  in  favour  of  a  chemical  theory. 

(1)  Thermo  chemical  reactions  of  fibres. 

(2)  Increased  affinity  shown  by  ammonia  treated 
cotton. 

(3)  Action  of  the  oxides  of  tin. 

The  chief  arguments  in  favour  of  chemical 
action  are  summed  up  by  v.  Georgievics  as  follows  : 

(1)  Magenta,  methyl  violet  and  chrysoidine  are 
decomposed   by   silk   and   wool,   hydrochloric   acid 
remaining  in  solution. 

(2)  Rosaniline     base     is    colourless.     The    salts 
are  coloured.     Wool  is  coloured  when  dyed  from 
an  ammoniacal  solution  of  the  base  (Jaquemin). 

(3)  The  red  solution  of  amidoazobenzenesulphonic 
acid  dyes  a  yellow  shade.     This  is  the  colour  of  its 
salts. 

(4)  Picric  acid  and  Naphthol  Yellow  are  taken 

15 


226         CHEMISTRY  AND  PHYSICS  OF  DYEING 

up  in  quantities  proportional  to  their  molecular 
weights. 

(5)  The  thermo- chemical  reactions  of  the  fibres. 

It  is  pointed  out,  however,  that  the  decomposition 
of  the  basic  dyes  is  brought  about  also  in  the  presence 
of  porous  inorganic  materials,  as  the  following  figures 
will  show.  The  presence  of  an  animal  fibre  is  not 
necessary. 


Colouring-matter. 

Amount 
taken. 

Cl  in  same, 

Colour  left 
in  sol, 

Cl  left  in 
sol. 

Magenta 

.2045 

.0166 

.08 

.0158 

Methyl  violet 

.2007 

.0152 

.09 

.0152 

Chrysoidine 

.2015 

.0309 

.122 

.0265 

It  will  be  seen  that  the  proportion  of  colour 
base  taken  up  by  the  porous  material  is  53  per  cent, 
against  only  8  per  cent,  of  the  chlorine. 

Glass  beads  will  act  in  the  same  way,  decompos- 
ing the  hydrochloride  of  the  base.*  Wool  takes  up 
more  hydrochloric  acid  at  45°  than  at  100°  C,  so 
does  porcelain. 

It  is  said  that  a  rosaniline  base  can  exist  in  two 
forms,  and  that  the  base  is  dark  violet  if  precipitated 
in  neutral  solutions.  The  base,  therefore,  may  exist 
in  two  forms :  (i)  As  carbinol  (colourless) ;  (2)  As 
ammonium  base  (coloured). 

A  colourless  aqueous  solution  of  the  base  does 
not,  therefore,  exist  as  Knecht  states,  and  Jacque- 

*  It  has  recently  been  stated  that  Jena  glass  will   not   act  in 
this  way,  owing  probably  to  its  great  insolubility. 


EVIDENCE  OF  CHEMICAL  ACTION   IN   DYEING     227 

min's  experiments  may  be  explained  as  follows. 
The  wool  and  silk  absorb  the  base  from  the  solution, 
and  since  the  alkali  is  not  taken  up  by  the  fibre  the 
wool  is  coloured  red. 

There  seems  to  be  some  doubt  as  to  the  existence 
of  the  coloured  ammonium  base.  H.  Weil  considers 
that  the  colour  is  due  to  unchanged  magenta  in  the 
precipitate. 

V.  Baeyer  (Ber.  1904;  2849)  also  doubts  the 
existence  of  v.  Georgievics'  coloured  ammonium  base. 

Hantzsch  (Ber.  1900,  752),  on  the  other  hand, 
holds  that  the  rosaniline  bases  are  capable  of 
existing. 

(i)  True  colour  base  : 


H;N.C6H4 
(2)  Pseudo  ammonium  base  : 


(3)  Imide  or  anhydride  base  : 
H,N.CflH  c/^-=-\. 
H2N.C(;H4>  -\=/ 

Further  work  on  the  absorption  of  dyes  by  in- 
organic substances  has  been  undertaken  by  Gmelin 
and  Rotheli  (Zeit.  f.  angew.  Chem.  1898,  482). 

Glass  beads  were  dyed  for  eleven  weeks  under 
identical  circumstances  with  (i)  Magenta ;  (2)  Ma- 
genta and  ammonia ;  (3)  Rosaniline  base.  They 
were  all  dyed  to  the  same  shade. 

Each  lot  was  then  washed  with  alcohol.  The 
two  last  lots  soon  lost  their  colour.  The  first  kept 
its  colour  for  some  time,  and  was  even  then  not 
decolourised. 


228         CHEMISTRY  AND  PHYSICS  OF  DYEING 

It  is  argued  from  these  results  that  magenta 
may  dye  in  two  ways,  the  one  chemical,  and  the 
other  mechanical. 

These  results  are  held  to  confirm  the  existence 
of  two  states  of  one  magenta  base,  and  that  the 
carbino]  base  is  fairly  stable,  and  requires  strong 
acids  to  convert  it  into  the  ammonium  base.  The 
conversion  of  the  one  into  the  other  in  the  presence 
of  silk  is  explained  by  assuming  that  the  silk  acts  as 
an  acid. 

Some  experiments  on  the  alkylation  of  magenta 
compounds  also  seemed  to  point  to  chemical  action. 
A  skein  of  silk  dyed  with  magenta  was  allowed 
to  stand  in  the  cold  in  contact  with  methyl  iodide 
in  methyl  alcohol.  Side  by  side,  and  in  the  same 
mixture,  were  rosaniline  base,  rosaniline  hydro- 
chloride  (magenta),  rosaniline  stearate,  and  the 
amido-stearate  of  the  same  base. 

The  only  change  noticed  was  the  alkylation  of 
the  rosaniline  base.  This  changed  to  a  deep  blue. 
The  inference  is  that  the  magenta  is  present  in  the 
silk  in  a  state  corresponding  to  the  hydrochloride, 
stearate,  &c.  In  other  words,  it  is  combined  with  the 
silk.  Unfortunately,  it  was  not  proved  at  the  same 
time  that  the  insoluble  basic  salts  act  in  the  same 
way  as  the  base  itself,  and  not  as  the  normal  hydro- 
chloride.  Until  it  is  settled  that  the  magenta  is  not 
present  in  this  state  on  the  silk,  these  results  are 
inconclusive.  At  a  temperature  of  35°-4o°  C 
alkylation  took  place  in  all  cases.  They  all  turned 
dark  blue. 


EVIDENCE  OF  CHEMICAL  ACTION   IN   DYEING     229 

The  colour  of  amidoazobenzenesulphonic  acid  on 
the  fibre  is  held  by  v.  Georgievics  to  be  yellow  because 
the  amount  of  dye  present  is  not  sufficient  to  dye  it 
red. 

Attempts  have  been  made  by  Prudhomme  (Rev. 
Gen.  des  Mat.  Col.  1900,  4,  189)  to  replace  the  fibre 
by  a  liquid  for  experimental  purposes,  with  the 
object  of  studying  the  results  obtained  under  these 
conditions.  Taking  a  solution  not  miscible  with 
water,  he  dissolved  salicylic  acid  or  a  weak  base 
(acetanilide)  in  the  same.  A  substance  like  phenylgly- 
cocoll  may  be  added  containing  both  basic  and  acid 
groups.  "  Dyeing  "  with  basic  colours,  different  shades 
to  those  of  the  solution  were  obtained  in  the  "  artifi- 
cial fibre."  They  corresponded  with  those  obtained 
on  silk  with  the  same  dyes.  Similar  results  were 
obtained  with  the  sulphonated  acid  colours,  using 
acetanilide  as  the  "  artificial  fibre."  That  silk  and 
wool  behave  like  amyl  alcohol  containing  the  above 
substances  is  the  conclusion  drawn  from  these  ex- 
periments. 

The  presence  of  salt-forming  groups  in  the  alky- 
lated  diazo  direct  dyes  is  said  to  be  proved  (Mayer 
and  Schafer,  Ber.  27,  3355),  and  this  is  put  forward 
as  a  possible  explanation  of  the  absorption  of  these 
dyes  by  cotton. 

The  impurities  present  in  the  cotton  fibre  may 
influence  its  dyeing  properties  in  some  cases. 
Schunck  suggested  (/.S.C./.,  815),  that  this  should 
be  tested  by  dyeing  samples  of  the  cotton  after  each 
of  the  following  operations ;  treatment  with  carbon 


230         CHEMISTRY  AND  PHYSICS  OF  DYEING 

disulphide,  alcohol,  boiling  water,  hydrochloric  acid, 
and  then  alkali. 

The  evidence  in  favour  of  the  presence  of  carboxyl 
groups  in  the  silk  molecule  is  fairly  satisfactory. 
Carboxyl  compounds  are  formed  when  silk  is  decom- 
posed by  barium  hydroxide  (Schutzenberger  and 
Bourgeois),  and  by  dilute  sulphuric  acid  (Cramer), 
or  alcoholic  potash  (Richardson). 

The  result  of  dyeing  wool  with  both  acid  and  basic 
dyes  at  the  same  time,  seems  to  offer  some  support  to 
the  chemical  theory.  Weber  shows  that  this  may  be 
done  if  a  skein  of  wool  be  dyed  with  Scarlet  R.  After 
being  carefully  washed,  it  will  take  up  magenta.  The 
percentage  of  this  second  dye  will  also  be  the  same 
as  that  taken  up  by  a  white  skein.  Furthermore, 
the  lakes  produced  by  the  combination  of  acid,  and 
basic  dyes  are  soluble  in  alcohol,  but  this  solvent 
will  not  remove  these  dyes  from  the  fibres. 

It  has  not  yet  been  shown  that  a  second  acid  dye 
will  not  enter  a  saturated  fibre  already  dyed  with  a 
colour  of  this  class,  or  that  a  basic  dye  will  not  ad- 
here to  a  basic  dyed  fibre.  This  would  necessarily 
follow  if  the  second  colour  did  not  displace  the 
original  one.  Further  work  is  necessary  before  these 
points  can  be  cleared  up. 

Weber's  statement  that  the  benzidine  dyes  are 
attracted  both  in  the  free  state  and  as  salts,  is  con- 
firmed by  Gmelin  and  Rotheli  (Zeit.  /.  angew.  Chem. 
1898,  482).  The  barium  salts  of  benzopurpurin 
4B  and  benzoazurin  %G  were  prepared  in  as  pure 
a  state  as  possible.  They  both  dyed  cotton,  and 


EVIDENCE  OF  CHEMICAL  ACTION   IN  DYEING     231 

subsequent  analysis  proved  that  the  dye  was  present 
on  the  fibre  as  the  barium  salt,  and  that  no  decom- 
position had  taken  place  during  the  process  of  dyeing. 
Owing  to  their  reduced  coefficients  of  diffusion 
they  dyed  very  slowly.  Correspondingly  they  did 
not  bleed  when  once  on  the  fibre. 

A  microscopical  examination  of  fibres  in  sections 
gives  the  following  results  :  Wool  dyed  with  Crystal 
Violet  or  Malachite  Green  shows  equal  distribution 
of  dye  throughout  the  fibre. 

Cotton  dyed  with  the  direct  dyes  shows  in  cross 
section  that  the  dyes  are  more  concentrated  in  the 
centre  of  the  fibre. 

Under  the  same  conditions  silk  seems  to  be  dyed 
equally  throughout.  A  similar  result  was  noticed 
by  the  writer  with  the  primuline  dyes  in  the  case 
of  silk. 

Returning  to  the  basic  dyes,  these  authors  pre- 
pared the  salts  of  palmitic  and  stearic  acids,  and 
dyed  silk  with  them.  The  fibre  was  then  dissolved 
in  hydrochloric  acid,  but  no  fatty  acids  could  be 
traced  in  the  solution. 

They  also  record  the  fact  that  the  benzidine 
salts  of  Naphthol  Yellow  S  were  decomposed  on 
dyeing,  the  benzidine  remaining  in  the  solution. 

This  is,  perhaps,  the  place  to  notice  some  ex- 
periments of  Schunck  and  Marchlewski  (J.S.D. 
and  C.  1894,  95).  The  tinctorial  effect  of  plant 
extracts  is  greatly  increased  by  boiling  with  acids, 
and  the  conclusion  arrived  at  is  that  the  effect  pro- 
duced is  due  to  the  decomposition  of  the  glucoside 


232         CHEMISTRY  AND  PHYSICS  OF  DYEING 

and  rhamnosides  of  the  colour-substances  present 
in  the  extracts.  It  is,  therefore,  necessary  to 
assume  hydrolysis  to  explain  the  actions  noticed  in 
practice  when  glucosides  are  used  in  dyeing. 

It  has  been  assumed  that  chrome  mordants  split 
up  the  glucosides  in  dyeing,  and  fix  their  colour 
constituents  only  (Hummel  and  Liechti). 

The  authors  find  that  in  practice  this  assumption 
is  correct.  In  dyeing  cotton  with  datiscin,  rutin 
and  quercitrin  the  sugar  is  left  in  the  solution. 
In  the  case  of  ruberythric  acid  the  decomposition 
did  not  take  place. 

It  will  be  seen  from  the  facts  recorded  in  the 
last  two  chapters,  that  the  evidence  brought  forward 
to  prove  that  the  action  of  dyeing  is  a  chemical  one, 
is  both  voluminous,  and  diverse,  in  its  nature,  and 
that  many  of  the  facts  which  at  first  sight  seem  to 
support  this  hypothesis  appear  less  definite  on 
further  examination. 

One  of  the  most  striking  examples  of  this  is  seen 
in  the  fact  that  such  an  inert  substance  as  porcelain 
will  split  up  the  basic  hydrochlorides,  in  much  the 
same  way  as  silk  will  do  under  similar  conditions. 

The  base  may  be  held  by  combination  in  the 
second  case ;  but  it  is  clear  that  the  action  may  take 
place  in  the  absence  of  any  organic  matter  whatso- 
ever, be  it  an  amido-acid,  or  of  any  other  constitution. 

It  is  therefore  a  matter  of  difficulty  to  give 
to  the  recorded  facts  their  true  significance. 

The  fact  that  most  of  the  work  done  on  this 
subject  is  of  a  qualitative  nature,  whilst  in  many 


EVIDENCE  OF   CHEMICAL  ACTION   IN  DYEING     233 

cases  the  reagents,  and  fibres,  are  in  an  unknown 
condition  of  purity,  greatly  increases  the  difficulty 
of  the  problem. 

It  is  not  possible  therefore  to  do  more  than 
record  the  results  obtained  in  many  cases,  and 
leave  the  future  to  sift  out  the  grain,  and  carefully 
weigh  it  as  evidence  against  the  facts  which  seem 
to  favour  a  wider  theory  of  dyeing. 

It  would  seem  that  generally  speaking,  certain 
facts  indicate  that  dyeing  may  be  due  to  chemical 
action ;  but  it  is  an  exceedingly  difficult  thing  to 
prove  from  these  that  the  action  is  really  of  this 
order. 

Until  the  time  comes  when  we  are  able  to 
explain  the  actions  which  take  place  when  colloids 
react  in  the  presence  of  solvents,  and  definitely 
assign  to  these  phenomena  their  true  value,  it  will 
be  difficult  to  establish  a  strictly  chemical  basis  for 
the  reactions  which  take  place  in  dyeing ;  or  even 
to  prove  that  such  action  is  a  determining  factor 
in  the  processes  of  dyeing,  mordanting,  and  the 
formation  of  certain  lakes. 


CHAPTER  X 

PART   PLAYED  BY   COLLOIDS  IN  DYEING  AND 
LAKE  FORMATION 

IT  will  have  been  gathered  from  the  reactions  shown 
by  colloids  in  general,  and  from  the  fact  that  both 
dyes  and  fibres  belong  to  this  class,  that  the  part 
played  by  these  bodies  in  dyeing  may  be  an  import- 
ant one. 

It  has  even  been  suggested  that  the  fixation  of 
the  dye-stuff  on  vegetable  fibres  is  analogous  to 
the  act  of  diffusion  through  colloids.  This  idea 
was  first  put  forward  by  Muller  Jacobs  (Text.  Colour- 
ist,  Oct.  and  Nov.  1884). 

Some  time  before  this  Schumacher  (Physik  der 
Pftanze\  experimenting  with  such  typical  colloids 
as  starch,  cellulose  fibre,  membranes,  &c.,  noticed 
that  there  was  not  only  an  absorption  of  liquids, 
but  also  of  the  solids  in  solution.  He  noticed  that  : 

(1)  The  relative  absorption  of  solids  is  greater, 
the  more  dilute  the  solution. 

(2)  The  absorption  decreases  as  the  temperature 
increases. 

(3)  Total  exhaustion  does  not  take  place  even 
in  very  dilute  solutions. 


COLLOIDS   IN   DYEING  AND   LAKE   FORMATION   235 

These  results  are  applied  to  the  absorption 
phenomena  of  vegetable  fibres,  and  an  attempt 
made  to  explain  the  action  of  dyeing  with  these 
fibres,  which,  unlike  the  animal  ones,  do  not  so 
directly  absorb  ordinary  acid  and  basic  dyes,  and 
therefore  cannot  be  so  readily  brought  into  line 
with  any  so-called  chemical  theory. 

This  explanation  of  the  action  of  dyeing  there- 
fore originated  in  an  attempt  to  explain  more 
particularly  the  specific  action  of  vegetable  fibres 
towards  dye-stuffs. 

To  accept  this  theory  we  must  allow  that  the 
action  of  dyeing  is  due  to  the  separation  of  the 
sparingly  soluble  colloid  dye  from  the  diffusible 
crystalloid,  or  solvent,  by  the  dialytic  action  of  the 
membrane  itself  ;  which  then  becomes  obstructed, 

(1)  by  the  formation  of  insoluble  precipitates  ; 

(2)  by  the  gradual  obstruction  of   the  colloids 
in  the  interstices  of  the  fibres. 

In  order  to  dissolve  these  sparingly  soluble  or 
non-permeable  bodies,  we  must  first  dissolve  them 
in  crystalloids  or  easily  permeable  solvents. 

Dr.  Jacobs  describes  an  interesting  series  of 
experiments  with  the  artificial  membranes  obtained, 
when  a  concentrated  and  neutral  solution  of  alu- 
minium sulphate  is  introduced  into  a  not  too  dilute 
solution  of  Turkey  Red  oil.  Membranes  are  in  this 
way  formed  round  the  drops ;  and  the  diffusion  of 
substances  through  them  can  be  easily  observed. 
For  instance,  when  alizarine  is  mixed  with  the 
outer  solution  the  colour  diffuses  into  and  colours 


236         CHEMISTRY  AND  PHYSICS  OF  DYEING 

the  cell  walls,  but  there  is  a  total  absence  of  colour 
in  the  interior  solution.  These  experiments  were 
carried  further,  and  alizarine  and  a  neutral  solution 
of  alumina  gave  a  red  lake  in  the  cell  wall,  but 
here  again  the  interior  remained  colourless. 

This  investigator  proposed  the  following  classifi- 
cation of  dyes  in  the  place  of  Bancroft's  scheme, 
which  divide  them  into  substantive  and  adjective 
colours : 

(1)  Such    substances    as    easily    pass    through 
colloids  or  fibres. 

(2)  Such    substances    as    pass     with    difficulty 
(colloids). 

(3)  Substances  which  will  not  pass  at  all. 
These  classes  are  not  considered  to  be  distinct 

but  to  merge  into  one  another  and  overlap. 

The  object  of  dyeing  is,  therefore,  to  fix  certain 
substances  within  the  fibre  in  such  a  way  that  the 
fibre  cannot  be  easily  deprived  of  them  by  the  action 
of  solvents.  The  means  by  which  this  action  may 
take  place  are  considered  to  be 

(1)  By  producing  precipitates  in  the  fibre. 

(2)  By  complete  separation  of  a  sparingly  soluble 
colloid  from  the  diffusible  crystalloid  or  solvent,  by 
the  dialytic  action  of  the  membrane  itself. 

The  mordanting  and  dyeing  actions  are  therefore 
considered  by  this  investigator  to  be  based  on  the 
action  of  two,  or  more,  differently  permeable  bodies. 
It  is  claimed  also  that  this  action  may  even  give  rise 
to  actual  decomposition  of  certain  chemical  com- 
pounds. 


COLLOIDS   IN  DYEING  AND  LAKE  FORMATION    237 

The  action  of  mordants  in  the  fibre  is  a  double 
one.  It  may  either  form  precipitates  with  the  dyed 
material,  or  else  reduce  the  permeability  of  the 
fibre  substance. 

The  reason  why  vegetable  fibres  do  not  dye  easily 
is  also  explained  by  assuming  that  they  are  more 
easily  permeable  than  the  other  fibres.  This  is 
perhaps  not  the  generally  recognised  view  of  the 
case. 

Similarly,  mercerising  or  oxidation  of  the  fibre 
does  not  act  by  reducing  this  action,  but  by 
increasing  it  in  some  cases. 

The  presence  of  albumin,  casein,  &c.,  on  the 
fibre  increases  the  colloidal  nature  of  the  fibre,  and 
therefore  the  laws  of  dialysis  will  produce  more 
powerful  effects. 

In  this  way  Miiller  Jacobs  attempts  to  explain 
the  action  of  dyeing. 

The  effect  of  tannic  acid  in  its  mordanting 
action  is  to  narrow  the  interstices  of  the  fibre,  and 
then  combine  with  the  dye  to  form  a  precipitate. 
The  proof  of  this  action  is  said  to  be  demonstrated 
by  the  fact  that  in  dyeing  alizarine  on  an  aluminium 
mordant  the  latter  must  be  present  in  great  excess. 
Fifteen  times  the  alumina  necessary  to  form  the 
normal  salt  (C14H6O2.A12O5)  must  be  present  to 
give  the  best  result. 

The  action  of  acids,  tartar,  &c.,  is  said  to  prevent 
the  superficial  fixing  of  colours. 

An  attempt  to  extend  this  theory  to  the  animal 
fibres  is  based  on  the  fact  that  oiled  cotton  will  dye 


238          CHEMISTRY  AND  PHYSICS  OF  DYEING 

red  with  rosaniline  hydrochloride.  It  is  considered 
that  this  is  evidence  that  the  dyeing  of  animal  fibres 
is  not  a  chemical  action. 

In  this  and  in  other  ways  this  theory  is  supported. 
For  instance,  many  organic  colloids  are  hardly 
diffusible  into  animal  fibres  owing  to  their  insoluble 
nature.  The  sulpho-acids  of  these  substances  being 
more  soluble  in  water  give  better  results.  They 
can  more  readily  penetrate  the  fibres.  Alizarine 
carmine  and  sulph-indigotine  are  given  as  examples. 
They  are  both  more  soluble  than  alizarine  and 
indigo,  and  therefore  dye  the  fibres  in  a  more 
satisfactory  way. 

On  the  other  hand,  these  sulpho-acids  may  be 
too  diffusible  for  vegetable  fibres. 

Assuming  also  that  the  dyes  become  more  like 
precipitates,  as  their  nature  becomes  more  compli- 
cated, and  as  the  amount  of  carbon  they  contain 
increases,  it  might  be  expected  that  the  complex 
members  of  a  group  of  colouring-matters  would 
require  to  be  present  as  sulpho-acids  for  dyeing 
purposes.  This  seems  to  be  the  case  with  the  rosani- 
lines. 

The  ami  do-benzenes  are  also  quoted  as  an  example. 

(1)  Amido-azobenzenes  (Aniline  Yellow)  is  spar- 
ingly fixed  on  cotton  even  as  the  sulpho-acid. 

(2)  Diamido  -  azobenzene      (Chrysoidine)     dyes 
cotton  well. 

(3)  Triamido  -  azobenzene    (Phenylene     Brown) 
dyes  well. 

This  action  with  the  sulphonic  acids   is   not   a 


COLLOIDS   IN   DYEING  AND   LAKE   FORMATION    239 

general  one.  For  instance,  the  indulines  are  in- 
soluble, and  sulpho-acids  form  more  or  less  readily, 
but  these  will  not  dye  cotton.  It  is  considered 
that  they  are,  in  this  case,  too  diffusible. 

The  general  conclusions  arrived  at  were  as 
follows.  The  permeability  of  a  substance  increases 
with  rise  in  temperature,  and  fibres  with  narrow 
interstices  require  a  higher  temperature  in  dyeing. 
Wool  would  come  into  this  class.  It  is  also  con- 
sidered that  when  mordanted  cotton  is  dyed  at  a 
low  temperature,  the  relatively  large  interstices 
become  smaller  by  deposition  of  the  dye-stuff,  and 
then  a  gradual  rise  in  temperature  is  required  to 
complete  the  dyeing  operation. 

If,  on  the  other  hand,  the  cotton  is  immersed 
initially  in  the  boiling  dye-bath,  the  colour  will  pass 
through  these  large  interstices,  and  the  material 
remain  undyed.  The  mordant  in  this  case  is 
dehydrated,  and  the  colour  cannot  be  fixed. 

From  this  point  of  view  the  case  of  the  colour- 
less sulphonic  acids  and  their  absorption  is  of  in- 
terest. Is  dehydrothiotoluidine  sulphonic  acid  the 
only  one  in  a  highly  colloidal  state  ?  This  might 
be  capable  of  direct  proof.  This  theory  has  been 
roughly  outlined.  Further  particulars  will  be  found 
in  the  original  papers. 

There  is  direct  evidence  from  the  work  of 
Picton  and  also  from  that  of  Krafft  (Ber.  1899, 
32,  1608),  that  high  molecular  dye-stuffs,  such 
as  the  direct  azo  dyes,  are  colloids. 

A  series  of  experiments  with  Magenta,  Methyl 


240          CHEMISTRY  AND  PHYSICS  OF  DYEING 

Violet  and  Methylene  Blue  gave  values  by  the 
ebullioscope  in  alcoholic  solutions  very  near  to  the 
true  molecular  weights.  In  water,  however,  the 
colloidal  state  is  taken  up. 

This  result  may  be  due  to  dissociation,  and  the 
less  soluble  nature  of  the  base ;  or  perhaps  to  asso- 
ciation. 

It  is  interesting  to  note  also  that  tannic  acid 
is  said  to  be  a  very  perfect  colloid  (Strutz  and 
Hofmann),  and  to  consider,  as  we  have  done  else- 
where, the  action  of  this  acid. 

In  the  case  of  wool  and  silk,  Krafft  considered 
that  the  fibre  itself  takes  part  in  the  interaction  in 
dyeing ;  but  that  in  the  case  of  cotton  the  action 
is  of  a  more  indeterminate  nature. 

We  may  learn  much  concerning  the  properties 
of  colloids  in  the  hydrogel  state,  and  their  action, 
from  a  study  of  the  phenomena  which  occur  in  the 
formation  of  coloured  lakes,  for  pigments  and  print- 
ing purposes.  This  subject  has  been  more  or  less 
exhaustively  studied  from  the  practical  point  of 
view  by  O.  Weber.  The  results  in  detail  may  be 
studied  in  the  original  papers. 

It  is  well  known  that  basic  dyes  (hydrochlorides) 
will  fix  themselves  on  indifferent  substances,  such 
as  starch,  cellulose,  alumina,  china  clay,  &c.  In 
this  way  pigments  may  be  formed. 

The  dyes  are,  however,  very  loosely  held,  yield- 
ing readily  to  water.  They  are  also  very  fugitive 
to  light  (Weber,  J.S.C.I.  10,  896). 

It  is  also  noticed  that  these  dyes  do  not  give 


COLLOIDS   IN   DYEING  AND   LAKE   FORMATION    241 

identical  shades  on  these  different  media.  This 
effect  is  also  noticed  in  the  case  of  dyeing  on 
fibres,  with  this  class  of  dyes.  The  shades 
obtained  on  cotton,  wool,  and  silk,  will  often 
materially  differ  from  one  another,  so  that  this 
action  seems  to  be  a  general  one.  The  student 
will  at  once  realise  the  general  nature  of  these 
dyeing  operations. 

It  is  interesting  to  note  that  tannic  acid,  which 
has  been  of  great  value  in  the  dyeing  of  cotton 
with  basic  dyes,  is  not  much  used  in  the  pro- 
duction of  lakes.  When,  however,  the  manufac- 
turers will  trouble  to  prepare  their  basic  lakes  in 
this  manner,  they  are  well  repaid.  The  fastest 
possible  lakes  are  produced  from  these  dyes  in  this 
way. 

The  fact  that  those  lakes  produced  in  indifferent 
substances,  are  so  extremely  fugitive  under  the 
action  of  light  deserves  attention.  A  comparison 
between  their  fastness  on  textile  fibres,  and  on  the 
indifferent  substances,  should  be  of  interest. 

It  is  noticed  also  that  the  attraction  which 
these  inert  substances  have  for  basic  dyes  is  modified 
by  the  nature  of  the  acids  which  enter  into  their 
constitution. 

Roughly  speaking,  the  amount  of  dye  fixed  is 
inversely  proportional  to  the  respective  strengths  of 
the  acids,  with  which  the  bases  are  in  combination. 
As  a  proof  of  this  Weber  gives  the  following  results, 
which  show  the  relative  amounts  of  colour  taken 
up  by  100  parts  of  alumina.  Under  the  standard 

16 


242          CHEMISTRY  AND  PHYSICS  OF  DYEING 

condition  of  the  tests  2  grams  of  alumina  were  sus- 
pended in  500  cc.  of  water. 

Colour  used.  Absorbed  by  100  pts.  A12O3. 

Bismark  Brown  G.  8.3 

Acetate  of  Magenta  7.13 

Methyl  Violet  B.  4.87 

Brilliant  Green  3.85 

Magenta  3.53 

Indazine  M.  1.96 

Methylene  Blue  B.  1.62 

Thioflavine  T.  1.43 

Solid  Green,  Cryst.  1.21 

Safranine  G.G.S.  .83 

There  seems  to  be  a  good  deal  of  evidence  to 
prove  that  these  dyes  when  present  on  inert  sub- 
stances are  in  the  form  of  basic  salts,  varying  in 
constitution  between  the  normal  salts,  and  the  bases 
themselves. 

That  they  are  not  present  as  simple  colour  bases 
is  proved  by  the  fact  that  the  bases  themselves  are 
for  the  most  part  colourless.  This  fact  is  to  be 
remembered  in  connection  with  the  dyeing  of  these 
colours  on  fibres.  These  basic  salts,  unlike  the 
normal  ones,  are  very  insoluble  in  water.  For 
example,  a  "  dissociation  "  lake  may  be  produced 
on  china  clay  by  precipitating  Benzaldehyde  Green 
in  the  presence  of  Glauber's  salt,  or  acetate  of  soda. ; 
With  this  reduction  in  the  "acidity"  of  these 
precipitated  basic  compounds,  a  corresponding  loss 
in  intensity  of  colour  is  noticed.  The  lakes  pro- 
duced in  this  way  are  partly  decolourised,  and  an 
addition  of  tannic  acid  will  develop  the  colour  in 
some  cases  to  the  extent  of  fifty  per  cent. 


COLLOIDS   IN   DYEING    AND  LAKE   FORMATION    243 

If  one  of  these  basic  lakes  be  washed  with  boil- 
ing water,  only  traces  of  colouring-matter  go  into 
solution,  and  the  lakes  ultimately  become  colour- 
less. In  the  same  way,  tannic  acid,  by  reducing 
the  basicity  of  the  colour  salt,  will  bring  the  colour 
back  to  a  great  extent.  This  reaction  is  important 
and  the  action  of  solvents  on  basic  dyes  present 
in  the  fibre  area  cannot  be  correctly  estimated  by 
the  altered  colour-effect  produced  in  this  way. 

It  is  known  to  every  silk  dyer,  that  washing  with 
water  will  decrease  the  intensity  of  the  shade  in  many 
cases,  and  a  subsequent  treatment  with  weak  acid 
will  bring  the  colour  back.  This  subject  should 
receive  further  attention.  Light  should  be  thrown 
on  the  state  in  which  these  dyes  are  present  in 
the  silk  fibre.  In  the  formation  of  lakes  with 
tannic  acid  the  action  seems  to  be  of  an  indefinite 
nature  (O.  N.  Witt).  The  amount  of  tannic  acid 
required  to  produce  a  true  lake  of  a  thoroughly 
saturated  nature,  as  compared  with  the  amount 
required  to  precipitate  the  basic  dye  perfectly  from 
an  aqueous  solution,  is  indicated  in  the  following 
table. 

Colouring-matter.  T'  ^  actually  T.  A.  required  for 

absorbed.  mere  precipitation. 

Magenta        .  .  .  622  ..  173 

Methyl  Violet  .  .  510  . .  138 

,v     Solid  Green  .  .  1324  ..  456 

Methylene  Blue  .  .  620  . .  198 

Chrysoidine  .  .  322  . .  194 

Weber  was  unable  to  indicate  the  course  taken 
by  the  interaction  between  the  dye  and  tannic 


244          CHEMISTRY  AND  PHYSICS  OF  DYEING 

acid.  It  does  not  follow  in  the  lines  of  chemical 
attraction,  as  indicated  by  the  constitution  of  these 
dyes.  The  action  seems  rather  to  be  on  the  lines 
of  colloid  precipitation,  and  may  be  regulated  by 
the  state  of  the  precipitate.  For  instance,  100 
parts  of  the  magenta  tannic  acid  compound  will 
absorb  160  extra  parts  of  tannic  acid  if  present  in 
excess,  while  100  parts  of  the  chrysoidine  tannic 
acid  compound  will  only  absorb  60  extra  parts  of 
tannic  acid  under  the  same  conditions. 

The  fact  that  the  tannates  of  antimony,  zinc, 
tin,  lead,  or  iron  will  give  better  and  faster  lakes 
than  tannic  acid  alone  (Witt)  is  an  interesting  point. 

Many  organic  acids  form  lakes  (or  insoluble 
compounds)  with  the  basic  dyes,  and  nearly  all  the 
aromatic  acids  act  in  this  way.  A  similar  result 
is  also  obtained  with  phosphoric  acid,  arsenious 
acid,  or  silicic  acid  when  present  as  their  alkaline 
salts. 

The  action  of  albumin  on  some  dyes  is  of 
interest.  For  instance,  Diamine  Scarlet  B 

C6H4.N  =  N  —  C0H4.O.C2H5. 

QTT 

C6H4.N  =  N-C10H4;SQ3Na 
SO3Na 

gives  a  very  clear  solution,  and  is  not  precipitated 
by  dilute  acids.  If  this  be  added  to  a  solution 
of  albumin  a  decided  precipitate  is  obtained.  It  is, 
however,  very  difficult  to  filter,  being  of  a  slimy 
nature.  To  precipitate  all  the  dye  a  large  excess 
of  albumin  is  necessary.  If,  however,  the  solution 


COLLOIDS   IN  DYEING  AND  LAKE  FORMATION     245 

be  heated  to  80°  C  the  albumin  coagulates,  and 
carries  down  with  it  the  whole  of  the  dye,  in  the 
form  of  brilliant  scarlet  flakes. 

If  this  precipitate  is  boiled  with  water  it  will 
give  up  some  of  its  colour  to  the  solution.  The  lake 
is  also  slowly  decomposed  by  soap  solution  at  50°  C. 
The  lake  on  drying  gives  a  heavy  solid,  which  shows 
little  sign  of  swelling,  or  solution,  in  water,  and  soap 
solution  at  80°  C  scarcely  affects  it. 

Acetic  acid  may  take  the  place  of  heat  in  pre- 
cipitating the  lake,  but  this  acid  will  not  precipitate 
either  the  dye,  or  the  albumin  by  itself. 

This  action  is  not  confined  to  direct  dyes.  Sul- 
phonated  basic  dyes,  azo  dyes,  and  sulphonated 
nitro  bodies  act  in  the  same  way. 

It  would  seem  that  for  two  substances  of  the 
above  nature  to  "  precipitate  "  one  another,  one 
of  them  must  be  in  a  state  near  to  the  point  where 
actual  precipitation,  or  coagulation,  takes  place. 
Gelatin,  for  instance,  is  incapable  of  this  precipi- 
tating action,  but  albumin  in  a  sensitive  condition, 
at  either  80°  C  or  in  the  presence  of  cold  acetic 
acid,  will  precipitate  the  dye. 

The  influence  of  the  dye  itself  also  helps,  or 
retards,  this  action.  Diamine  Scarlet  will  precipi- 
tate albumin  in  the  cold.  Eosine,  on  the  other 
hand,  will  only  act  in  this  way  at  a  high  temperature. 

It  is  said  that  the  shades  obtained  correspond 
exactly  with  those  obtained  on  wool,  or  silk. 

If  the  basic  dye  had  combined  with  the  albumin 
in  the  cold,  a  precipitate  would  probably  have  been 


246  CHEMISTRY  AND  PHYSICS  OF  DYEING 

formed,  and  this  indicates,  so  far  as  it  goes,  that  the 
action  between  the  albumin  and  the  basic  dye  is  not 
of  a  chemical  nature. 

For  some  reason  the  fastness  against  light  of 
these  precipitated  lakes  varies  with  the  nature  of 
the  precipitant.  Albumin  lakes  are  said  to  be  four 
times  as  fast  as  the  corresponding  barium  lakes, 
using  the  same  dyes.  The  extremely  fugitive 
nature  of  the  basic  dyes  on  a  china  clay  basis  has 
been  already  noticed. 

This  may  be  due  to  two  causes : 

(1)  Difference  in  size  of  the  dye  aggregates. 

(2)  Difference  in  the  way  the  dyes  are  held. 
Arguing    from    the   extraordinary   sensitiveness 

of  diazotised  primuline,  when  produced  in  a  colloid 
substance,  the  size  of  the  aggregates  may  affect  the 
action.  The  matter  is  one  which  demands  attention, 
and  a  further  study  of  this  matter  may  lead  to 
interesting  results. 

Surface-Concentration  and  Devolution  Effects.— 
A  modified  theory  on  the  above  lines  was  recently 
brought  forward  (Dreaper,  J. S.C.I.  1905,  233), 
to  explain  the  general  action  of  dyeing.  It  is 
founded  on  the  work  of  Linder  and  Picton  (J.C.S. 
1892,  61,  148  and  1895,  63)  and  others,  and  attempts 
to  explain  the  dyeing  action  on  lines  which  are 
usually  regarded  as  physical,  although  it  is  not 
denied  that  chemical  action  may  supplement  the 
actions,  which  lead  to  the  general  absorption  of  the 
dye  by  the  fibre. 

The  work    on    pseudo-solution  undertaken    by 


COLLOIDS    IN   DYEING  AND   LAKE  FORMATION    247 

Linder  and  Picton  has  hardly  received  the  notice 
it  deserves  by  those  interested  in  the  subject  of 
dyeing. 

The  dividing  line  between  perfect  solution,  and 
suspension  has  broken  down.  The  difference  be- 
tween the  two  states,  is  only  one  of  aggregation ; 
although  it  is  not  to  be  inferred  from  this,  that  any 
substance  may,  by  successive  stages,  pass  from  the 
former  to  the  latter  state.  This  action  is  neither 
a  reversible  one  in  many  cases,  nor  is  it  necessarily 
a  complete  one.  In  solutions  of  colloids  the  relation- 
ship between  the  solution,  and  the  colloid  (solute), 
is  never  complete,  as  in  the  case  of  a  crystalloid. 
Solution  stops  short  at  some  intermediate  stage, 
and  consequently,  as  has  been  explained  elsewhere, 
the  usual  phenomenon  of  a  lowered  freezing-point 
of  the  solution  is  not  in  evidence  to  the  same  degree 
as  in  a  perfect  solution  of  a  crystalloid.  So  far  as 
appearance  goes  there  is  little  difference  between  a 
colloid,  and  a  crystalloid  in  dilute  solutions ;  but  an 
examination  of  the  physical  properties  of  the  former 
in  solution  indicates  that  the  differences  in  the  solu- 
tion state  must  be  appreciable. 

An  interesting  case  of  a  colloid  in  a  state  of 
pseudo-solution  is  that  of  arsenious  sulphide,  which 
can  be  prepared  in  a  state  of  such  fine  suspension, 
that  the  solution  will  pass  easily  through  a  porous 
pot  without  separation  of  the  solid. 

This  is  in  itself  a  fact  of  general  interest,  but 
when  we  study  the  action  of  metallic  salts  on  these 
pseudo-solutions  the  results  at  once  become  of 


248  CHEMISTRY  AND  PHYSICS  OF  DYEING 

interest  to  the  dyer.  In  their  action  on  these  solu- 
tions, the  different  salts  divide  themselves  into 
sharply  denned  groups,  corresponding  with  their 
valency.  As  a  general  result  the  effect  of  the  addition 
of  these  salts,  is  to  degrade  the  state  of  the  pseudo- 
solution.  The  aggregates  become  larger  in  size,  and 
may  even  be  precipitated.  The  salts  of  tervalent 
metals  possess  the  highest  coagulating  power.  Biva- 
lent metals  only  act  with  one  tenth  of  the  effect 
and  univalent  metals  with  less  than  one  five- 
hundredth  part  of  the  intensity  in  the  first  case. 
This  difference  in  the  power  of  precipitation,  even 
extends  to  the  same  metal  when  the  valency  varies 
(e.g.,  with  iron).  One  molecule  of  aluminium  chloride 
possesses  the  same  coagulating  power  as  16.4  mole- 
cules of  cadmium  chloride,  or  750  molecules  of  sul- 
phuric acid. 

When  the  coagulating  action  of  salts  on  a  solu- 
tion of  arsenious  sulphide  is  studied  in  detail, 
unexpected  results  are  obtained.  As  an  example, 
when  barium  chloride  is  used  as  a  coagulating 
medium,  the  barium  is  carried  down,  and  the 
chlorine  left  in  solution.  Similar  results  are 
obtained  with  calcium  chloride.  The  precipitated 
metal  is  retained,  even  after  thorough  washing 
with  water,  but  another  salt  in  solution  will 
replace  it. 

This  action  is  one  of  mass,  and  is  not  due  to  selec- 
tive affinity,  as  it  is  reversible,  and  depends  entirely 
on  the  proportion  of  the  second  salt  in  solution.  For 
example,  both  calcium  and  cobalt  salts  will  coagu- 


COLLOIDS   IN   DYEING  AND  LAKE  FORMATION     249 

late  in  this  way,  yet  either  will  replace  the  other 
if  present  in  sufficient  quantity  in  the  solution. 

It  will  at  once  be  seen  that  the  influence  of  these 
experiments,  on  a  strictly  definite  chemical  theory 
of  dyeing,  is  a  disturbing  one.  A  theory  of  mass 
action  and  the  resulting  affinity  which  is  able  to 
disturb  such  a  system  as  that  represented  by 
barium  chloride  in  solution  might  clearly  take  the 
place  of  a  chemical  theory  of  dyeing,  and  explain 
the  experiments  of  Vignon  and  Knecht  on  the  one 
hand,  and  of  v.  Georgievics  on  the  other. 

It  will  be  seen,  that  we  may  equally  expect  a 
similar  action  with,  say,  rosaniline  hydrochloride. 
In  fact,  with  such  an  example  before  us,  we  can 
hardly  set  any  limit  to  this  action. 

Extending  their  experiments  to  other  substances 
Linder  and  Picton  found  that  dye-stuffs  such  as 
Hofmann's  Violet,  Methyl  Violet,  and  Magenta,  gave 
interesting  results. 

The  solutions  of  these  dyes  are  so  far  perfect 
that  the  aggregates  present  are  not  sufficiently  large 
to  scatter  light,  as  some  of  the  arsenious  sulphide 
solutions  do,  yet  they  were  non-filterable.  These 
results  are  altogether  abnormal,  from  the  point  of 
view  of  the  standards  set  up  by  these  investigators 
for  arsenious  sulphide  solutions,  and  we  are  clearly 
here  face  to  face  with  an  extension  of  the  action 
in  the  case  of  these  basic  dyes. 

Further  experiments,  however,  showed  that  the 
porous  material  itself  will  absorb  the  dye  if  broken 
pieces  of  it  were  left  in  the  dye  solution.  The 


250         CHEMISTRY  AND  PHYSICS  OF  DYEING 

authors  did  not  carry  these  experiments  to  their 
logical  conclusion,  by  identifying  the  action  as 
similar  in  its  nature  to  that  of  barium  chloride, 
or  they  would  have  looked  for  a  decomposition  of 
the  basic  hydrochloride  in  the  porous  material. 
The  cause  of  the  decomposition  of  basic  dye-stuffs 
in  this  porous  material  is  uncertain.  It  is  either 
due  to  a  colloid  state  set  up  on  the  surface  of 
the  porous  material,  or  else  is  due  to  "  surface 
action." 

Our  knowledge  of  the  actions  which  are  associated 
with  surfaces  is  incomplete,  at  the  present  time. 
It  is  possible  to  explain  them  in  the  following 
way.  The  material  of  which  a  porous  pot  is  com- 
posed, by  virtue  of  its  liberal  surface,  and,  as  we 
know,  slight  solubility,  will  present  to  the  solution 
a  large  surface  in  a  colloidal  state,  and  this  by  its 
action  may  decompose  the  basic  hydrochloride,  and 
precipitate  the  base. 

It  is  just  possible  that  capillary  action  may 
play  a  considerable  part  in  the  action.  It  must, 
however,  not  be  lost  sight  of,  that  this  action  is 
directly  connected  with  surface  action.  In  fact,  it 
is  caused  by  it.  The  secret  of  capillary  action  being 
the  greatly  increased  attraction  at  small  distances 
(Hawkesbee). 

The  dissociation  of  the  basic  dye  in  solution,  if 
it  takes  place,  and  its  influence  on  such  an  action 
as  the  above,  should  make  experiments  on  this  subject 
important.  Dyeing  fibres  and  porcelain  material, 
with  dyes  dissolved  in  mixtures  of  alcohol  and  water 


COLLOIDS   IN   DYEING  AND  LAKE  FORMATION    251 

in  varying  proportions,  should  be  undertaken,  and 
their  relative  actions  noticed. 

The  influence  of  the  addition  of  sodium  chloride, 
or  other  salts,  on  pseudo-solutions  of  arsenious  sul- 
phide is,  by  analogy,  of  great  importance. 

The  solution  becomes  non-filterable,  and  there- 
fore degraded  in  the  scale  of  solubility.  The  action 
of  such  substances  on  dye-solutions  is  well  known. 
The  importance  of  this  action  is  considered  by  the 
writer,  to  be  not  so  much  that  caused  by  a  decreased 
solubility  of  the  dye  in  the  solution,  as  the  solid 
solution  theory  requires,  but  that  the  increase  in 
the  size  of  the  aggregates  and  their  degradation  in 
the  scale  of  solution,  is  the  important  condition; 
and  that  this  is  the  cause  of  the  modified  result 
obtained  in  the  presence  of  a  suitable  fibre. 

Furthermore,  the  effect  produced  by  filtration 
shows  that  the  degradation  of  the  arsenious  sulphide 
solution  is  specific.  The  effect  is  as  if  all  the 
aggregates  present  are  increased  in  size. 

From  this  and  other  considerations,  the  writer 
has  put  forward  the  hypothesis  that  in  any  system 
of  a  hydrosol,  and  to  a  modified  extent  in  the  case 
of  a  hydrogel,  the  size  of  the  aggregates  is  determined 
by  the  two  factors,  the  mutual  attraction  of  the 
molecules  and  the  solvent  action  of  the  solution. 
This  latter  factor  may  be  the  attraction  of  the  solute 
molecules  for  those  of  the  solution.  When  an  equili- 
brium is  actually  set  up  between  these  two  opposite 
forces,  the  aggregates  will  be  of  a  definite  size,  and 
remain  so  until  the  system  is  modified  by  some 


252          CHEMISTRY  AND  PHYSICS  OF  DYEING 

secondary  action,  and  the  colloid  either  degraded 
in  the  scale  of  solubility,  or  the  reverse. 

It  will  be  seen  that  the  action  of  salts  on  a 
solution  of  a  direct  dye  is  capable  of  explanation. 
It  has  already  been  pointed  out  that  the  direct 
dyes  do  not  give  true  solutions  in  water.  That 
is  to  say,  they  give  pseudo-solutions.  The  action 
of  salts  should  give  the  same  results  in  both  cases, 
and  there  is  no  evidence  at  present  that  such  is 
not  the  case. 

The  influence  of  different  solvents  on  the  mole- 
cular weights,  or  size  of  the  aggregates,  is  undoubted. 
For  instance,  the  following  table  shows  the  number 
of  double  molecules  of  nitrogen  peroxide  in  different 
solvents  (Walker). 

Solvent.  Double  mols.  at  20°.       Double  mols.  at  90°  C. 

Per  cent.  Per  cent. 

Acetic  acid          .  .     97.7  ...  95.4 

Ethylene  chloride  .95.8  ...  91.3 

Chloroform  .  .     92.3  ...  85.5 

Carbon  bisulphide  .     87.3  ...  77.5 

Silicon  tetrachloride  .     84.3  ...  77.4 

It  will  therefore  be  seen  that  for  some  reason, 
probably  owing  to  the  relative  attractions  between 
the  solvent  molecules,  and  those  of  the  solute,  the 
state  of  aggregation  varies  greatly  with  different 
solvents.  In  the  case  quoted  the  state  of  aggrega- 
tion is  never  very  great,  at  least,  as  compared  with 
that  known  to  exist  in  the  case  of  the  so-called 
colloids,  but  it  will  sufficiently  well  indicate  the 
action  which  takes  place. 

The  influence  of  increased  temperature  may  also 


COLLOIDS   IN   DYEING  AND   LAKE   FORMATION     253 

be  indicated  in  terms  of  the  molecular  state  of  the 
solution. 

The  increase  in  molecular  weight  in  more  concen- 
trated solutions,  is  indicated  also  in  the  case  of  a 
solution  of  alcohol  in  benzene,  and  for  this  purpose 
the  following  table  is  quoted. 

Concentration.  Mol.  weight 

Per  cent.  (Alcohol  =  46). 

494      •  -.      5° 

2.29         .  .  .-.  .  .  .82 

3.48 .100 

8.8        .         .        .        .        .        .         .     159 

14.6        .         .         .         .        *        .         .     209 

This  would  also  seem  to  indicate  that  association 
increases  with  molecular  strength  of  solution. 

Effect  of  concentrated  solutions. — The  increased 
effect  produced  in  concentrated  solutions  of  dyes  is 
also 'explained  by  assuming  that  the  size  of  aggre- 
gates is  constant  in  any  solution  of  this  nature.  From 
this  point  of  view,  the  aggregates  are  larger  rather 
than  more  numerous  in  the  more  concentrated 
solution. 

So  that  we  have  alternate  means  of  producing 
larger  aggregates. 

(1)  By  degrading  the  solution  by  means  of  the 
addition  of  salts. 

(2)  By  increasing   the  concentration  of   the  dye 
solution. 

Both  of  these  methods  answer  in  practice,  but 
as  will  be  pointed  out  later  on,  the  former  is 
likely  to  be  the  more  efficient,  owing  to  the  addi- 
tional effect  produced  by  "  surface  concentration/' 


254          CHEMISTRY  AND  PHYSICS  OF  DYEING 

and,  in  practice,  the  saving  in  dye  material  is  an 
important  factor. 

We  know  that  molecular  aggregation  extends 
to  the  state  we  call  solution,  and  this  is  a  further 
proof  that  there  is  no  dividing  line  between  a  colloid 
and  a  perfect  solution. 

It  is  therefore  suggested  that  the  aggregates 
are,  within  certain  limits,  constant  in  number  rather 
than  in  size,  as  the  strength  of  the  solution  alters. 

With  increased  concentration,  there  comes  a  time 
when  the  aggregates  are  so  large  that  their  relations 
to  the  solvent  assume  a  new  phase.  The  point  at 
which  they  occupy  a  space  larger  than  the  physical 
conditions  of  the  liquid  will  allow  may  be  a  critical 
one.  In  crystalloids,  which  do  not  pass  through  the 
colloid  state,  but  are  controlled  in  their  desolution 
by  molecular  forces  which  directly  determine  their 
ultimate  solid  state,  this  point  is  a  sharp  one,  and 
gives  rise  to  a  separation  of  the  salt,  probably  in 
the  crystalline  form. 

With  colloids,  or  substances  which  take  a  hy- 
drated  form,  the  course  adopted  is  a  different  one, 
and  between  the  pseudo-solution  state,  and  that 
of  the  absolutely  dry  substance,  there  is  no  sharply 
defined  dividing  line ;  but  merely  a  slow  passage 
from  one  state  to  the  other  as  determined  by  the 
relative  proportion  of  water  molecules  present, 
although  the  actual  point  at  which  the  hydrosol 
is  coagulated,  may  be  a  critical  one. 

With  decreased  amount  of  solvent  certain 
other  phenomena  come  into  more  active  play,  and 


COLLOIDS   IN   DYEING  AND   LAKE   FORMATION     255 

an  automatic  separation  of  the  colloid  material  may 
actually  take  place  from  these  secondary  causes. 

Closely  connected  with  the  subject  of  the  con- 
stant size  of  the  aggregates  in  a  hydrosol  is  the 
mechanism  by  which  this  can  be  determined ;  here 
we  must  assume  molecular  migration  (Dreaper, 
J.S.D.  and  C.  1905). 

This  is  not  an  impossible  condition.  Actual 
atomic  migration  has  already  been  assumed  by 
Poisson,  and  this  being  so,  it  is  held  by  the  writer 
that  the  forces  which  are  called  molecular  are  similar 
in  their  nature  to  those  which  are  called  atomic. 
Such  a  migration  is  a  necessary  adjunct  to  any 
theory  of  association  between  a  liquid,  and  a  solute. 

There  is  also  a  certain  amount  of  evidence  that 
these  changes  do  occur  in  a  solution,  and  that 
they  can  be  actually  observed,  as  the  case  of 
very  viscous  solutions,  like  those  of  nitrocellulose 
in  organic  solvents.  The  observed  fact  of  the 
"  ripening  "  of  such  solutions  is  held  to  be  due  to 
an  action  of  this  kind.  Several  months  elapse  in 
some  cases  before  the  ultimate  state  of  equilibrium 
between  the  solvent  and  solute  is  reached. 

If  we  assume  this  action,  it  is  also  possible  to 
explain  the  slow  dialysis  of  colloids  through  mem- 
branes, which  is  theoretically  possible,  and  has 
been  observed  in  the  case  of  nitrocellulose  by  de 
Mosenthal  (J.S.C.I.  1904,  292).  If  we  assume 
the  migration  of  individual  molecules  from  one 
aggregate  to  another,  it  is  possible  for  these 
aggregates  to  pass  gradually  through  a  membrane, 


256          CHEMISTRY  AND  PHYSICS  OF  DYEING 

by  some  such  secondary  action,  although  they 
themselves  are  incapable  of  passing  directly  from 
one  side  to  the  other. 

In  the  action  of  dyeing  there  is  a  constant  play 
of  altered  conditions  due  to  temperature,  alteration 
in  concentration,  &c.,  and  consequently,  a  constant 
variation  in  size  of  the  aggregates,  which  in  itself 
will  entail  this  roving  state  of  the  individual  mole- 
cules. 

It  has  also  been  established  by  Linder  and  Picton 
(ibid.)  that  a  4  per  cent,  solution  of  arsenious  sul- 
phide is  non- filterable  under  ordinary  conditions. 
This  would  indicate  that  the  aggregates  are  larger 
in  size,  and  support  the  above  conceptions. 

Support  is  seemingly  given  to  these  views  by 
the  observed  action  of  the  following  complicated 
and  obscure  cases  in  general  dyeing. 

If  a  logwood  iron  lake  be  dissolved  in  a  dilute 
solution  of  oxalic  acid,  it  will,  as  is  well  known,  dye 
silk  and  other  fibres  a  deep  black  colour.  In  its 
original  state  the  lake  is  insoluble.  The  particles 
or  aggregates  have  in  its  preparation  been  so  de- 
graded in  the  scale  of  solution,  that  they  are  no 
longer  within  the  limits  of  dyeing  requirements. 
By  the  gradual  addition  of  oxalic  acid  to  a  suspen- 
sion of  this  lake  in  water,  the  size  of  the  aggregates 
is  in  some  way  gradually  reduced,  passing  by  stages 
of  colour  from  black  through  brown  to  an  almost 
golden  colour,  as  the  proportion  of  oxalic  acid  is 
increased. 

Assuming  that  the  lake  in  its  more  soluble  state 


COLLOIDS   IN   DYEING  AND   LAKE  FORMATION    257 

passes  through  a  corresponding  state  of  pseudo- 
solution,  we  arrive  at  the  following  conclusions. 
The  aggregates  in  this  state  come  into  close  enough 
relation  with  the  fibre  substance  for  de-solution 
to  take  place  from  whatever  cause,  be  it  surface 
attraction,  or  concentration,  or  mass  attraction  at 
short  distance.  At  any  rate,  the  solution  state, 
whatever  it  be,  is  disturbed  by  the  presence  of  the 
fibre,  and  the  solution  state  is  degraded  with  the 
precipitation  of  the  lake  in  the  substance  of  the 
fibre.  Alizarine  lakes  in  the  "  one  bath  "  method 
of  dyeing  also  seem  to  act  in  the  same  way. 

From  the  above  theoretical  considerations,  it 
would  also  be  expected  that,  if  the  molecular  pro- 
portion of  oxalic  acid  be  increased,  a  point  will 
ultimately  arrive  when  from  one  cause  or  the  other 
a  decreased  de-solution  effect  will  be  produced. 
This  actually  occurs  in  practice. 

It  would  follow  also  that  at  this  stage  a  further 
addition  of  lake,  or  a  reduction  in  the  amount  of  free 
acid,  would  increase  the  size  of  the  dye  aggregates, 
and  cause  a  reversal  of  the  action.  This  is  also 
actually  observed. 

The  colour-effect  in  the  solution  is  also  completely 
reversible,  and  runs  parallel  with  the  dyeing  results. 

Under  certain  conditions  silk  and  wool  fibres 
are  capable  of  attracting  from  aqueous  suspension 
certain  insoluble  amines  (Pokorng,  Bull.  Soc.  Ind. 
Mulh.  1893,  282),  if  they  are  in  a  state  of  fine 
division. 

Naphthylamine,  if  dissolved  in  a  small  quantity 

17 


258          CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  alcohol,  and  poured  into  water,  will  impregnate 
wool  in  twelve  hours  in  the  cold. 

The  fixing  is  said  to  be  entirely  mechanical,  and 
the  amine  is  easily  removed  by  water. 

These  results  have  been  confirmed  by  P.  Werner 
(ibid.),  and  further  experiments  show  that  the  result 
is  directly  influenced  by  the  proportion  of  alcohol 
to  water.  As  the  alcohol  increases  from  5  to  30 
per  cent,  the  absorption  increases.  Beyond  this 
a  reverse  action  sets  in  on  similar  lines  to  that  of 
the  logwood-iron-lake  solution,  and  with  essentially 
different  substances  he  obtained  the  same  effect. 
As  the  alcohol  increases  so  does  the  solubility.  Up 
to  a  certain  point  this  leads  to  increased  dyeing 
effect.  Beyond  this,  the  action  of  the  alcohol  on  the 
hydrated  fibre  state,  and  the  decreased  size  of  the 
aggregates,  tell  against  absorption. 

The  action  of  a  more  efficient  solvent  (alcohol) 
on  dyes  in  fibres  is  to  reduce  the  size  of  the  aggre- 
gates. Under  these  circumstances  the  dye,  or  part 
of  it,  may  leave  the  fibre.  This  is  noticed  in  many 
cases,  and  it  tends  to  indicate  that  such  dyeing 
actions  in  mixed  solvents  is  more  due  to  the  solution 
state  than  to  the  fibre  state,  but  a  great  deal  more 
work  will  have  to  be  done  on  this  subject  before 
it  will  be  possible  to  apportion  to  each  action  its 
qualifying  effect. 

The  action  played  by  water  is  still  obscure. 
It  may  be  that  it  is  indicated  by  the  statement 
made  by  Pokorng,  that  while  pure  alcohol  will  not 
extract  some  dyes  from  the  fibre,  yet  95  per  cent. 


COLLOIDS   IN   DYEING  AND  LAKE  FORMATION    259 

alcohol  will  do  so.  (See  page  167.)  This  may  indi- 
cate that  the  pure  alcohol  cannot  enter  the  fibre, 
and  that  a  semi-hydrated  state  is  necessary  before 
the  colour  can  be  extracted.  Otherwise  some  more 
complicated  and  unknown  action  is  involved. 

Experimental  evidence  as  to  the  relative  solu- 
bility of  the  dyes  in  mixtures  of  alcohol  and  water, 
both  in  the  presence,  and  absence,  of  a  fibre  substance 
are  wanting.  Also  there  is  no  evidence  available 
to  show  whether  the  fibre  absorbs  more  water  than 
alcohol  from  mixtures  of  the  same.  Both  these 
points  will  be  made  the  subject  of  investigation. 

It  is  possible  that  the  dye  aggregates  are 
associated  with  solvent  molecules,  in  fact,  are  doubly 
complex  in  this  way.  The  same  applies  to  the 
fibre.  If  we  have  molecular  migration,  the  aggre- 
gates may  even  join  up  loosely  with  the  fibre  aggre- 
gates, and  in  this  way  the  fibre  and  dye  be  held 
together  by  some  such  secondary  attraction. 

The  third  case  given  as  evidence  in  favour  of 
these  theoretical  conclusions  is  taken  from  some 
work  done  by  Binz  and  Bing  (Zeit.  /.  angew.  Chem. 
25, 1902),  on  the  relative  action  of  salts  on  the  dyeing 
of  wool  with  indigo,  in  cases  where  the  alkalinity 
of  the  bath  varies. 

The  addition  of  neutral  salts,  such  as  Glauber's 
salt,  sodium  chloride,  &c.,  does  not  intensify  the 
shade  so  long  as  the  alkali  is  only  present  in  sufficient 
quantity  to  dissolve  the  indigo  white.  In  the  pre- 
sence of  excess  of  alkali,  the  addition  of  neutral 
salts  has  an  intensifying  action,  and  as  a  result, 


260         CHEMISTRY  AND  PHYSICS  OF  DYEING 

darker  shades  are  produced  on  the  fibre.  The 
presence  of  i-8  per  cent.  Nad,  for  instance,  doubles 
the  amount  of  indigo  absorbed  by  the  fibre. 

In  the  presence  of  a  large  excess  of  alkali,  this 
increased  dyeing  effect  on  the  addition  of  salts  is 
not  nearly  so  pronounced. 

It  is  not  difficult  to  see  that  here,  also,  we  may 
find  an  explanation  of  the  effect  of  these  substances 
in  the  presence  of  excess  of  alkali ;  when  the  state 
of  solution  is  of  a  more  perfect  nature,  it 
might  be  expected  that  the  action  of  salts  would 
be  correspondingly  reduced,  and  this  would  natur- 
ally effect  the  dyeing  result.  It  must  always  be 
remembered  that  the  fibre  state  may  also  be  pro- 
foundly modified  by  the  presence  of  these  substances 
in  solution. 

So  that,  as  is  pointed  out,  by  a  careful  adjust- 
ment of  the  excess  of  alkali  to  that  of  the  salt,  a 
satisfactory  state  of  the  fibre,  or  one  of  maximum 
absorption,  may  be  obtained,  and  the  best  dyeing 
effect  be  produced. 

This  is  the  condition  which  would  naturally  be 
aimed  at  by  the  practical  dyer,  from  the  point  of 
view  of  economy. 

It  is  of  great  importance  to  note  that  the  alkali 
is  evidently  not  fixed  on  the  fibre  in  any  way,  and 
it  is  only  necessary  to  take  account  of  the  fixation 
of  the  indigo  white.  V.  Georgievics  (Der  Indigo, 
1892,  55)  has  shown  that  it  is  only  the  latter  which 
is  fixed,  the  alkali  remaining  in  the  solution.  The 
results  obtained  by  Koechlin  as  a  result  of  a  study 


COLLOIDS  IN   DYEING  AND  LAKE   FORMATION    261 

of  the  absorptive  power  of  cotton  for  tannic  acid 
are  of  interest  from  this  point  of  view.  It  is  known 
that  tannic  acid  gives  pseudo-solutions. 

Experimenting  with  different  strengths  of  solution 
abnormal  results  were  obtained. 

The  point  of  maximum  absorption  seemed  to 
coincide  with  a  concentration  of  .2  per  cent. 
Beyond  this  reversal  seemed  to  set  in,  for  a  cotton 
saturated  in  a  .5  per  cent,  solution  still  absorbed 
tannic  acid  in  a  .2  per  cent,  solution.  The 
state  of  aggregation,  or  else  the  mutual  attraction 
of  the  tannic  acid  for  the  cotton  fibre,  is  altered 
subsequently  in  a  .02  per  cent,  solution,  for  in  this 
the  cotton  just  begins  to  lose  tannic  acid. 

If  figures  could  be  obtained  showing  the  relative 
action  of  cotton  and  mercerised  cotton  with  regard 
to  this  reversal,  the  results  would  be  of  interest.  In 
some  such  way  as  this  it  might  be  possible  to  indicate 
whether  the  action  was  due  to  the  fact  that  the 
latter  is  in  a  more  highly  colloidal  state,  or  whether 
the  additional  hydroxyl  groups  play  a  part  in  the 
action.  A  further  study  of  this  subject  is  contem- 
plated. 

It  has  already  been  noticed  that  the  addition  of 
acetic  acid  to  the  tannic  acid  solution  greatly  in- 
creases the  proportion  of  the  latter  acid  absorbed 
by  the  fibre.  Apart  from  the  value  of  this  observa- 
tion from  the  practical  point  of  view,  its  possible 
influence  on  our  knowledge  of  dyeing  is  obvious. 
The  action  is  as  difficult  to  explain  in  this  case 
as  in  the  case  of  silk  or  wool  dyeing  with  sulphonic 


262        CHEMISTRY  AND  PHYSICS  OF  DYEING 

acids,  or  carboxyl  dyes  in  the  presence  of  stronger 
acids. 

Surface  concentration  also,  as  the  writer  has 
pointed  out,  must  play  an  important  part  in  any 
theory  of  dyeing. 

If  the  action  of  dyeing  were  purely  chemical  in 
its  nature,  this  concentrating  effect  would  have  an 
important  bearing  on  the  rate  of  dyeing,  but  from 
the  point  of  view  of  pseudo-solution  it  occupies  a 
still  more  important  position. 

Assuming  that  dyeing  is  an  action  which  is 
independent  of  any  actual  attraction  between  the 
fibre  substance  and  the  dye,  it  is  very  difficult  to 
see  how  the  fibre  can  attract  the  dye,  or  hold  it. 

It  is  this  difficulty  which  made  Cross  and  Bevan 
(J.S.C.I.  13.  354)  accuse  O.  Weber  of  assuming 
a  one-sided  penetrability  for  the  dye  substance. 
That  is  to  say,  that  the  dye  would  diffuse  into  the 
fibre,  but  would  not  diffuse  out  again.  If,  however, 
one  realises  the  possibility  of  this  concentrating 
action  at  surfaces,  the  matter  at  once  assumes  a 
different  aspect. 

J.  J.  Thomson  (App.  of  Dynamics  to  Phys.  and 
Chem.,  p.  251)  pointed  out  that  the  most  stable 
arrangement  of  any  solution  will  be  accompanied 
by  minimal  surface  energy.  The  result  of  this 
action  is  distinctly  seen  in  practice.  There  is  a 
tendency  with  most  salts  to  concentrate  at  surfaces, 
and  for  a  similar  reason,  and  to  a  correspondingly 
greater  extent,  in  capillary  tubes. 

For   instance,  in  the  case  of   graphite  or  meer- 


COLLOIDS   IN   DYEING  A  ND  LAKE  FORMATION    263 

schaum,  this  concentration  in  the  case  of  potassium 
sulphate  is  nearly  25  per  cent. 

It  will  be  seen  that  the  influence  of  this 
action  in  dyeing  may  be  a  profound  one,  for  with 
the  additional  concentration  of  the  pseudo-solution 
of  the  dye  we  shall  have  a  rearrangement  of  the 
aggregates.  The  size  of  these  will  correspondingly 
increase  within  the  capillary  spaces  of  the  fibre 
substance  owing  to  this  action. 

The  rate  of  diffusion  will  correspondingly  de- 
crease, and  we  shall  arrive  at  a  state  where  the 
osmotic  action  is  greatly  in  excess  of  the  exos- 
motic  one.  This  can  produce  but  one  effect,  viz.,  a 
concentration  of  the  dye  substance  in  the  fibre  area, 
and  a  state  of  "  one-sided  penetrability"  is  arrived 
at.  When  it  is  also  recognised  that  the  salts  will 
also  concentrate  about  and  in  the  fibre  area,  it  is 
easy  to  realise  the  possible  result  of  this  general 
action. 

The  effect  of  the  concentration  of  the  assistant 
and  its  influence  on  the  state  of  aggregation 
may,  it  is  held,  be  seen  in  the  dyeing  of  silk 
with  ordinary  acid  colours.  If  the  dyed  silk  be 
introduced  into  water,  some  of  the  dye  is  readily 
removed.  With  the  decrease  in  the  concentra- 
tion of  the  acid  the  aggregates  may  decrease  in 
size,  and  be  partly  removed,  or  tend  to  re- 
enter  the  dye  solution.  This  action  is,  therefore, 
a  reversible  one. 

As  a  result,  therefore,  of  this  concentration 
effect,  it  is  obvious  that  the  dye  may  be  degraded 


264          CHEMISTRY  AND  PHYSICS  OF  DYEING 

in  the  scale  of  solubility  ;    that  it  may  actually 
become  insoluble. 

In  the  case  of  dyeing  with  logwood  lake  by  the 
aone  bath"  method,  the  fact  that  the  colour  of  the 
silk  fibre  is  not  black,  but  dark  brown,  until  the 
skein  is  finally  washed  in  water,  indicates  that 
the  dye  state  is  one  of  degradation,  rather  than 
complete  dissociation  from  the  solution  state  during 
the  time  of  dyeing. 

In  this  case  it  is  probable  that  the  concentration 
of  oxalic  acid  in  the  fibre  area  is  small  as  compared 
with  that  of  the  dye-stuff.  If  this  were  found  not 
to  be  the  case  it  might  indicate  that  some  secondary 
attraction  between  the  dye  and  fibre  substances 
comes  into  play,  and  to  that  extent  accounts  for 
the  displacement  of  the  equilibrium  of  the  dye 
solution  within  the  fibre  area. 

The  intensity  of  this  surface  concentration  varies 
with  different  acids  and  salts.  An  elaborate  series 
of  experiments  was  conducted  by  Gore  on  this 
subject  (Birmingham  Nat.  Hist,  and  Phil.  Soc.  IX.  i, 
1893).  The  effect  is  directly  dependent  on  the 
area  of  the  surface.  For  instance,  if  a  dilute  solu- 
tion of  acetic  acid  be  filtered  through  fine  white 
sand,  nothing  but  pure  water  will  percolate  through, 
the  whole  of  the  acetic  acid  being  kept  back  by 
this  action. 

The  following  results  chosen  at  random  from 
a  very  full  list  in  the  original  paper  will  illustrate 
the  relative  action  of  substances.  Ten  per  cent, 
solutions  were  used  in  each  case. 


COLLOIDS  IN   DYEING  AND  LAKE   FORMATION    265 

HC1    lost  2.88  per  cent.  Tartaric  acid  lost  1.42  per  cent. 

HI        ,,     i.o  „  Citric  acid       „     nil          ,, 

HN03,,     2.5  „  CaCl,  „     3.1 

HC1045,     4.4  „  NaCl  „     2.77        „ 

We  have  therefore,  a  physical  reason  for  the 
concentration  of  substances  in  solution  at  surfaces, 
and  the  influence  of  this  action  cannot  be  neglected. 

It  will  be  seen  that  this  is  still  more  evident 
when  it  is  noticed  that  this  tendency  to  concentrate 
is  stronger  in  the  case  of  substances,  in  a  state  of 
pseudo-solution,  than  with  salts  which  are  more 
soluble. 

In  the  case  of  substances  of  high  molecular 
weight  these  surface  concentrations  may  be  so  in- 
tensified by  mechanical  movement  that  the  sub- 
stances may  heap  up  and  form  visible  films  of  solid, 
or  very  viscous  matter  (Ramsden,  Proc.  Roy.  Soc. 

72,  156). 

The  size  of  the  aggregates  undoubtedly  affects 
the  general  result.  For  instance,  Gore  found  that 
the  following  substances  gave  positive,  or  negative 
surface  attraction  results,  as  indicated.  It  will  be 
seen  that  substances  in  suspension  give  abnormal 
results. 

Picric  acid  in  solution  ...  No  result 

„  in  suspension  .  ;  Result 

Salicylic  acid  in  solution  „  No  result 

„  in  suspension  .  .  .  Result 

Methyl  orange       .          .          .          .  „ 

Orange  G.  .... 

It  may  be  that  the  molecules  of  soluble  substances 
like,  say,  sodium  chloride  "salt  out"  dyes  by  means 


266         CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  the  greater  attraction  between  the  solution  and 
solute  molecules  in  the  case  of  more  perfect  solutions. 
In  the  case  where  these  colloid  substances  are  separ- 
ated by  the  above  mechanical  means,  they  are  not 
always  resoluble  in  the  solution.  They  are  some- 
times even  insoluble.  The  action  of  aggregation 
is  non-reversible  under  these  conditions. 

These  separated  films  vary  greatly  in  their 
physical  properties.  They  may  be  membranes, 
membrane-fibrous,  or  fibrous  as  the  case  may  be; 
or  they  may  even  consist  of  particles  lying  side  by 
side. 

The  special  surface  viscosity  which  accompanies 
these  separations,  and  which  is  indicated  by  a 
resistance  to  "  shear,"  develops  at  very  different 
rates. 

These  concentrations  also  occur  at  the  inter- 
surfaces  of  two  solutions,  and  give  rise  to  distinct 
surface  tension  phenomena  at  the  junction  of 
aqueous  colloid  solutions  of  different  concentrations 
(Quincke,  Drudcs  Ann.  10,  478). 

In  this  action,  coupled  with  the  above  laws  of 
aggregation,  and  possibly,  molecular  migration,  we 
have  an  explanation  which  will  satisfy  the  dyeing 
conditions  in  a  great  many  cases  such  as  the  "  one 
bath "  method,  indigo  and  Cf  sulphide "  dyeing, 
the  dyeing  of  direct  colours  on  cotton,  &c.,  without 
bringing  in  any  complication  due  to  chemical  action. 
Dr.  W.  H.  Perkin,  senr.,  has  pointed  out  (J.S.C.I. 
1905,  p.  235),  that  the  surface  character  of  silk, 
wool  and  cotton  respectively  can  be  shown  to  pro- 


COLLOIDS   IN   DYEING  AND   LAKE   FORMATION    267 

duce  different  results  under  the  following  conditions. 
A  skein  of  cotton  was  worked  for  some  time  in  an 
emulsion  of  olive  oil  and  carbonate  of  potash,  such 
as  was  used  by  Turkey-red  dyers.  On  wringing  it 
out  afterwards,  nothing  but  pure  water  left  the 
skein;  the  cotton  was  practically  free  from  oil. 

On  repeating  this  experiment  with  a  silk  skein 
the  water  was  still  nearly  pure,  but  the  silk  retained 
a  large  amount  of  oil. 

By  substituting  a  wool  skein  for  silk,  and  after 
rinsing  the  skein  in  water,  the  oil  ran  from  the  wool 
in  quantity  on  wringing. 

These  experiments  are  of  interest.  The  oil 
particles,  or  aggregates  are  of  course  much  larger 
than  in  any  case  of  pseudo-solution  met  with  in 
dyeing,  but  the  results  produced  show  the  very 
different  nature  of  the  absorption  of  such  substances 
by  these  three  typical  fibres,  and  also  indicate  that 
the  absorption  which  may,  in  this  case,  be  taken 
to  be  of  a  physical  nature,  is  very  pronounced. 

Dr.  Perkin  states  also  that  the  behaviour  of  these 
different  fibres  in  relation  to  the  oil  corresponds 
closely  to  their  dyeing  power.  This  would  not, 
however,  seem  to  be  a  universal  rule,  especially 
with  the  direct  colours,  yet  the  phenomena  recorded 
are  certainly  suggestive  in  their  nature. 

Some  experiments  of  Chabrie  (Comptes  Rend. 
115,  57)  roughly  indicate  the  limit  at  which  it  might 
be  expected  that  concentration  might  take  place 
in  the  fibre  area.  Experimenting  with  capillary 
tubes  of  a  diameter  of  .07  mm.,  interesting  results 


268         CHEMISTRY  AND  PHYSICS  OF  DYEING 

were  obtained;  on  passing  a  solution  of  albumin 
slowly  through  such  a  tube  a  separation  takes 
place,  and  only  pure  water  passes  through.  The 
albumin  is  concentrated  in  the  tube  to  such  an 
extent  that  ultimately  all  flow  is  stopped.  This 
would,  in  a  case  of  dyeing,  indicate  the  ultimate 
absorption  point,  or  the  dyeing  limit,  and  the  size 
of  the  inter-spaces  in  different  fibres,  and  of  the 
same  fibre  in  different  states  of  hydration,  would  of 
course  greatly  modify  the  action.  The  influence  of 
this  action  is,  therefore,  evident,  and  will  have  a 
definite  bearing  on  the  best  condition  of  the  fibre 
substance  for  dyeing  purposes,  the  object  being  to 
bring  the  greatest  possible  number  of  fibre  molecules 
in  contact  with  the  dye  aggregates  without  ultimate 
damage  to  the  fibre  itself  by  disintegration.  A 
good  example  of  this  action  is  seen  in  the  in- 
creased action  of  dyes  on  powdered  wool  under 
standard  conditions. 

In  the  cotton  fibre,  when  the  cellulose  which  has 
once  been  dried  is  not  easily  rehydrated,  the  aid  of 
hydrating  substances  is  necessary  to  obtain  the  best 
effect.  Mercerising  increases  the  power  of  the  fibre 
in  this  direction.  The  mass  action  of  a  fibre  will 
depend  on  its  original  construction  modified  by  its 
capability  of  entering  the  hydrogel  condition  in  the 
presence  of  water. 

Extended  treatment  with  water  itself  will,  to 
a  certain  extent,  take  the  place  of  the  action  of 
reagents  in  inducing  this  state.  Continued  boiling 
in  water  will  induce  this  state  in  the  cotton 


COLLOIDS  IN   DYEING  AND  LAKE   FORMATION    269 

so  that  its  attraction  for  certain  dyes  is  materially 
increased  (Hiibner  and  Pope). 

The  bleeding  of  direct  dyes  on  cotton  indicates 
that  the  dye  is  loosely  held,  in  fact,  very  much  in 
the  way  it  might  be  expected  if  the  dye  were  precipi- 
tated, or  held  by  de-solution,  and  subject  to  re- 
solution, either  by  molecular  migration,  or  otherwise. 

The  experiments  on  the  influence  of  temperature 
on  the  ultimate  dye  state  of  the  fibre  made  by  Brown 
indicate  some  such  action  as  the  above. 

When  the  solubility  of  a  dye  increases  with 
temperature,  we  may  assume  that,  in  the  case 
of  the  direct  dyes,  which  give  pseudo -solutions 
(Schultz),  the  aggregates  are  correspondingly  smaller 
at  higher  temperatures.  Keeping  this  in  mind,  let 
us  examine  the  results  obtained  with  Kalle's  Direct 
Yellow  G.  The  amount  of  dye  absorbed  by  silk, 
wool,  or  cotton  increases  up  to  80°  C.  Beyond  this 
point  the  curves  for  silk  and  cotton  turn  one  way, 
and  that  for  wool  the  other. 

In  the  case  of  a  fibre  which  gives  increased 
absorption  beyond  this  point,  we  must  either  have 
a  more  or  less  sudden  change  in  the  fibre  state,  or 
else  the  decrease  in  the  size  of  the  dye  aggregates 
will  allow  of  their  more  rapid  diffusion  into  the  fibre 
area. 

In  the  case  where  a  decreased  absorption  is 
recorded,  the  increase  in  dye  absorption  may  be 
due  to  the  aggregates  becoming  too  small  to  be 
degraded  in  the  fibre  substance  under  the  altered 
conditions.  Such  a  case,  where  the  absorption  of  a 


270         CHEMISTRY  AND  PHYSICS  OF  DYEING 

colour  by  silk  and  wool  becomes  greater  in  the  one 
case,  and  decreases  in  the  other,  does  not  support 
a  theory  of  dyeing  which  assumes  a  common  cause 
of  attraction  (tyrosine)  in  these  two  fibres.  The 
action  may  be  complicated  by  changes  in  the  fibre 
state,  and  it  is  necessary  to  consider  the  possibility 
of  dissociation  effects. 

The  writer  has  for  some  time  sought  an  explana- 
tion of  the  abnormal  fastness  of  Night  Blue  on  silk 
fibres  against  the  action  of  boiling  soap  solution, 
in  light  shades.  In  darker  colours  the  fastness  is 
not  anything  like  so  pronounced.  Up  to  a  certain 
shade  the  dye  will  withstand  a  treatment  extending 
over  half  an  hour.  It  would  seem  that  here  we 
have  a  case  of  dyeing,  where  the  dye  is  held  in  two 
ways.  The  first  portion  is  either  in  a  very  degraded 
state  of  solution,  or  else  it  is  held  by  direct  attraction 
or  affinity. 

This  may  be  one  of  the  cases  in  which  dyeing 
is  in  one  stage  a  process  of  chemical  action. 
Taking  everything  into  account,  the  writer  suggests 
that  the  natural  order  of  the  phenomena  which 
take  place  in  dyeing  is  something  of  the  following 
nature,  depending  on  the  factors  ; 

(1)  A  solution  state  of  the  dye,  within   certain 
limits   of  aggregation,   determined  by   the  laws   of 
size. 

(2)  A  fibre  state  corresponding  to  this    state  of 
aggregation,  and  of  a  permeable  nature. 

(3)  Effective  localisation  of  the  dye  within  the 
fibre  area,  due  to  surface  concentration  phenomena. 


COLLOIDS   IN   DYEING  AND  LAKE  FORMATION    271 

(4)  Localisation  of   any  salts,  acids,  &c.,  within 
the  fibre  area. 

(5)  The  indirect  entrance  of  the   dye   aggregate 
by  molecular  migration,  with  subsequent  reforma- 
tion of   an  even  more  complex    nature  within  the 
fibre  area,  under  conditions  mentioned  under  (4). 

(6)  De-solution,    due    to     secondary     attraction 
between   the   fibre   substance   and   the   dye,   or  by 
reduced  surface  energy  phenomena,  or  concentration 
effects. 

(7)  In  some  cases,  primary  or   chemical    action 
may  play  some  part  at  this  stage.     This  may,  even  in 
some  cases,  take  the  place  of  de-solution  phenomena. 

(8)  In  the  case  of  basic  dyes,  dissociation  effects 
may  lead  to  the  isolation  of  very  basic  salts  in  a 
state  of  high  aggregation  within  the  fibre  area. 

We  have  seen  that  barium  chloride  and  other 
salts  undergo  decomposition  in  the  presence  of 
colloids,  like  arsenious  sulphide.  It  is,  therefore, 
not  to  be  wondered  at  if  actual  decomposition 
of  the  basic  hydrochlorides  takes  place  within 
the  fibre  area.  It  is  known  that  these  dyes  suffer 
decomposition  of  a  partial  nature,  at  any  rate,  by 
capillary  action.  It  is  also  well  known  that  the 
basic  dyes  become  very  insoluble  when,  by  losing 
part  of  their  hydrochloric  acid,  they  become  basic 
salts. 

It  is  not  difficult  to  indicate  a  state  of  affairs 
which  would  offer  a  satisfactory  explanation  of  the 
fixing  of  these  dyes  in  animal  fibres,  or  degraded 
hydrogels,  or  even  in  the  pores  of  such  a  com- 


272          CHEMISTRY  AND  PHYSICS  OF  DYEING 

paratively  inert  substance  as  porcelain,  or  china 
clay. 

It  is  difficult  to  imagine  that  the  action  of 
dyeing  is  a  strictly  chemical  one.  For  instance, 
it  is  noticed  that  in  mordanting  cotton  with  tannic 
acid  the  best  results  are  obtained  by  immersing  the 
cotton  in  the  boiling  solution  and  allowing  it  to  cool. 
The  mordanting  takes  place  at  the  lower  temperature. 
The  solution  of  tannic  acid  will  be  of  a  more  perfect 
nature  at  higher  temperatures,  and  therefore  the 
aggregates  will  be  correspondingly  smaller.  They 
will  increase  in  size  as  the  solution  cools,  and  there- 
fore become  more  readily  fixed,  especially  if  they 
re-form  within  the  fibre  area.  This  action  is  recorded 
by  Brown  (J.S.D.  and  C.  1901,  p.  94),  and  is  an 
interesting  one,  which  is  comparable  in  many  ways 
to  the  reduced  dyeing  effect  noticed  in  certain  cases, 
at  temperatures  above  80°  C. 

The  solvent  action  of  alcohol,  or  benzene,  on  dyes 
which  are  already  fixed  on  the  fibre  is  an  indication, 
perhaps,  that  these  dyes  are  chiefly  held  by  de- 
solution  rather  than  by  any  process  of  primary,  or 
chemical  attraction. 

In  the  presence  of  a  solvent  of  higher  power  the 
aggregates  are  correspondingly  smaller.  A  new 
system  is  set  up,  and  the  dye,  or  part  of  it,  leaves 
the  fibre.  There  is  no  question  here  of  solid  solution, 
but  simply  that  of  solution  following  de-solution. 

The  direct  fixation  of  the  dye  may  be  due  there- 
fore to  three  causes  : 

(i)  De-solution,  including  dissociation  effects. 


COLLOIDS   IN   DYEING  AND   LAKE  FORMATION    273 

(2)  Pseudo  or  secondary  action. 

(3)  Primary  or  chemical  action. 

These  three  phenomena  may  overlap  each  other, 
there  being  no  strict,  or  hard  and  fast  division 
between  them.  It  is  held  that  there  is  evidence  to 
indicate,  that  all  substances  during  precipitation 
pass  through  the  pseudo  solution  state. 

An  equilibrium  between  the  relative  attraction  of 
the  solution  and  solute  molecules,  on  the  one  hand, 
and  the  molecular  attraction  of  the  solute  molecules 
for  each  other  will  be  established  in  any  system. 

In  the  case  of  very  insoluble  compounds  the 
solution  attraction  is  unable  to  break  down  the 
aggregates  of  the  solute  beyond  a  certain  point. 

In  some  cases,  and  by  certain  means,  an  abnormal 
state  of  aggregation  may  be  induced  in  the  case  of 
these  very  insoluble  substances,  and  we  then  arrive 
at  a  condition  which,  as  in  the  case  of  some  metals, 
is  regarded  as  the  colloid  state.  Analogy  would 
suggest  that  this  state  is  equivalent  to  the  state  of 
supersaturation  in  the  case  of  a  crystalloid,  or  a  gas. 

At  this  point  in  the  case  of  a  dye  which 
is  in  a  state  of  pseudo-solution,  the  only  change 
which  will  take  place  will  be  due  to  molecular  migra- 
tion owing  to  local  influences;  or  to  the  tendency 
to  set  up  an  ultimate  state  of  equilibrium  over 
the  whole  system. 

Such  is  the  de-solution  theory  advanced  to  explain 
the  action  of  dyeing.  The  chief  objection  to  it 
is,  perhaps,  that  this  action  will  be  of  too  irregular 
a  nature  to  explain  the  definite  results  obtained 

18 


274         CHEMISTRY  AND   PHYSICS   OF  DYEING 

in  some  cases,  which  indicate  that  the  ratio  of 
absorption  of  certain  dyes  is  in  direct  relation  to 
the  combining  weights  of  the  dyes  absorbed. 

It  has,  however,  been  recently  shown  (see  p.  121) 
that  the  salts  of  calcium,  strontium,  barium  and 
potassium  are  precipitated  by  colloids  in  the  ratio 
of  their  chemical  equivalents  (J.  Billitzer,  Zeit. 
Phys.  Chem.  1903,  45,  307). 

The  phenomena  which  present  themselves  in  the 
presence  of  pseudo-solutions  are  sufficiently  well 
marked  to  demand  attention. 

The  conditions  of  surface  concentration  have 
been  observed,  and  studied  from  a  mathematical 
point  of  view  ;  the  experimental  results  recorded 
are  beyond  dispute. 

The  fact  that  de-solution  may  take  place  in  the 
presence  of  a  liberal  surface  has  also  been  observed 
in  the  case  of  pseudo-solutions. 

The  action  of  precipitating  agents  on  colloids 
is  a  definite  one,  as  shown  by  the  replacement  of 
one  metal  by  another,  under  the  laws  of  mass  action, 
as  recorded  by  Linder  and  Picton,  and  the  addi- 
tional statement  made  by  Billitzer,  that  the  different 
metals  are  originally  precipitated  in  the  ratio  of 
their  chemical  equivalents,  when  they  are  carried 
down  by  the  degraded  colloids.  These  precipitating 
actions  are  clearly  definite,  although  they  may 
not  be  strictly  chemical  in  their  nature. 

This  phenomenon  of  de-solution  is,  it  is  held,  seen 
in  the  remarkable  result  obtained  by  Hallett  on 
dissolving  the  colour  off  dyed  yarn. 


COLLOIDS   IN   DYEING  AND  LAKE  FORMATION    275 

When  dark  shades  of  indigo  were  stripped  in 
this  way,  the  dye  extracted  by  the  solvent  was  also 
thrown  out  in  the  insoluble  form  as  a  precipitate. 
So  that  we  have  here  a  system  where  the  one-bath 
method  of  dyeing  may  be  seen  reversed.  Start- 
ing with  the  dye  already  fixed  on  the  fibre,  the 
conditions  of  dyeing  may,  from  this  point  of  view, 
be  so  far  realised,  that  a  condition  of  equilibrium 
may  be  established  in  which  the  indigo  may  be 
present  on  the  fibre,  in  solution,  and  in  the  insoluble 
state  as  an  actual  precipitate. 

The  suggestion  I  have  made,  that  an  arsenious 
sulphide  solution  may  be  regarded  as  equivalent 
to  an  "  artificial  fibre  substance,"  and  that  if  we 
can  have  such  an  action  with  barium  chloride,  a 
similar  action  with  a  basic  hydrochloride,  or  even  a 
sulphuric  acid  salt  is  quite  possible,  has  recently 
received  confirmation  (see  p.  278).  W.  Biltz  (Chem. 
Centr.  19052,  524)  has  shown  that  if  the  ordinary 
dyeing  process  be  represented  by  the  formula 

Cn  fibre 
C  dye  liquor  ' 

where  C  fibre  is  the  concentration  of  dye-stuff  in 
the  dyed  fibre,  C  dye  liquor  is  that  in  the  dye-bath, 
and  the  index  n  is  greater  than  i  (it  is  frequently 
found  to  be  a  whole  number),  then  working  with 
inorganic  colloids  and  a  suitable  dye-stuff,  there 
is  no  essential  difference  between  the  dyeing 
properties  of  coloured  inorganic  colloidal  substances 
and  organic  dye-stuffs. 

The   comparative   experiments   were    conducted 


276          CHEMISTRY  AND  PHYSICS  OF  DYEING 

with  benzopurpurin  on  the  one  hand,  and  molyb- 
denum blue,  and  vanadium  pentoxide  on  the 
other. 

In  both  cases  the  composition  of  the  coloured 
fibre  after  dyeing,  at  a  given  temperature,  depends 
on  the  conditions  of  the  dyeing  process,  the  con- 
centration of  the  dye-stuff,  and  the  nature  of  the 
salts  added  to  the  dye-bath. 

Furthermore,  with  the  substitution  of  the  hy- 
drogel  of  alumina  for  the  organic  fibre  the  same 
relations  hold. 

In  the  same  way  some  experiments  made  by 
W.  Biltz  and  P.  Behre  (ibid.)  with  dialysed  solutions  of 
Immedial  sulphur  dye-stuffs,  which  were  free  from 
alkaline  sulphides,  showed  that  these  dyes  were 
"coagulated"  (or  salted  out)  by  electrolytes,  and  that 
the  coagulating  power  of  these  substances  increased 
with  the  valency  of  the  cathion.  This  same  effect, 
it  will  be  remembered,  is  noticed  in  the  coagulating 
experiments  with  arsenious  sulphide  solutions. 

Again,  in  the  case  of  these  dyes  similar  absorp- 
tion results  were  obtained  when  the  hydrogels  of 
alumina,  zirconium  dioxide,  ferric  oxide,  and  stannic 
oxide  were  substituted  for  textile  fibres. 

In  this  way  the  experimental  results  have  shown 
that  in  the  cases  under  consideration  there  seems 
to  be  a  direct  relation  between  the  dyeing  of  the 
fibre,  and  that  of  inorganic  hydrogels. 

It  is  interesting  to  note  that  in  the  original  work 
on  the  subject  of  the  absorption  of  inorganic  colloids 
by  fibres  (Biltz,  Chem.  Centr.  1904,  i,  1039),  the 


COLLOIDS   IN   DYEING  AND  LAKE   FORMATION    277 

absorption  is  also  increased  by  the  addition  of  salt 
to  the  solution. 

The  general  conclusions  arrived  at  were  that, 
by  comparison,  the  solutions  of  the  organic  dye- 
stuffs  were  subject  to  more  complete  exhaustion 
than  those  of  the  inorganic  colloids,  and  that  the 
shades  produced  are  faster  against  washing,  and 
rubbing.  The  addition  of  electrolytes  to  the  solu- 
tion led  to  more  complete  absorption  in  both 
cases.  Increasing  the  temperature  of  the  dye-bath 
also  has  the  same  general  effect. 

Weighted  silk  had  an  increased  affinity  for 
inorganic  and  organic  colloids.  The  absorption 
was  retarded  by  the  presence  of  '  protective  col- 
loids "  in  both  cases. 

A  direct  comparison  between  the  dyeing  action 
of  molybdenum  blue,  vanadium  pentoxide,  ruthenium 
oxychloride,  and  silver,  with  benzopurpurin  also 
indicated  that  they  were  of  the  same  order  when 
dyed  on  silk  and  cotton.  The  concentration,  con- 
dition, and  additions  to  the  dye  liquor  affected  the 
results  (Ber.  1905,  2963). 

The  hydrogel  alumina  absorbed  methylene  blue, 
colloidal  silver,  and  benzopurpurin ;  the  fibre  being 
replaced  by  this  inorganic  hydrogel  without  the 
absorption  effect  being  altered. 

In  the  case  of  the  sulphur  dyes  colloidal  solu- 
tions were  prepared  by  dialysing  solutions  for 
ten  to  fourteen  days.  Cotton,  aluminium  hydrate, 
ferric  hydrate,  and  oxide  of  tin,  absorbed  the  dyes 
from  these  solutions  (Ber.  1905,  2973). 


278         CHEMISTRY  AND   PHYSICS  OF   DYEING 

Certain  absorption  results  may  take  place  with 
inorganic  colloids,  which  have  been  long  recognised 
in  the  preparation  of  lakes.  The  absorption  seems 
to  be  of  the  same  order  as  that  which  occurs  in  the 
dyeing  of  silk,  or  cotton  with  certain  colours. 

If  the  inorganic  colloids  are  in  the  hydrosol 
state  they  may  be  absorbed  by  fibres  or  inorganic 
colloids.  They  may  even  be  carried  down  by 
barium  sulphate. 

If  the  inorganic  colloids  are  in  the  hydrogel 
state,  they  may  absorb  dyes  in  the  same  way  as 
fibres. 

Quite  recently  Linder  and  Picton,  returning 
to  this  subject  (Trans.  Chem.  Soc.  1905,  1930),  show 
that  ferric  hydroxide  is  coagulated  by  a  solution 
of  Soluble  Blue,  C38H28N3(SO3Na)3,  or  Nicholson's 
blue  (C37H28N3.SO3Na)  in  the  same  way  as  it  is 
by  ammonium  sulphate. 

At  a  certain  critical  point  a  red  coagulum 
separates  which  contains  all  the  iron  and  the  sul- 
phonic  acid,  an  equivalent  amount  of  sodium 
chloride  remaining  in  solution. 

After  extraction  with  alcohol  a  red  precipitate 
remains,  which,  is  decomposed  by  dilute  sulphuric 
acid,  or  salt  solution.  The  hydrox3r-ctye-sulphonate 
is  decomposed.  The  solution  takes  a  deep  blue 
colour. 

With  Methyl  Violet,  C19H12(CH3)5N3.HC1,  no 
coagulation  takes  place.  Chlorides  only  coagulate 
ferric  hydroxide  in  highly  concentrated  solutions.  . 

With  arsenious  sulphide  the    order  is  reversed. 


COLLOIDS   IN   DYEING  AND  LAKE  FORMATION     279 

With  Methyl  Violet  a  hydrosulphide  derivative 
is  precipitated  and  hydrochloric  acid  remains  in 
solution.  Aniline  Blue  has  no  such  power,  but 
sodium  salts  only  coagulate  arsenious  sulphide  in 
highly  concentrated  solutions.  Hofmann's  Violet 
or  Magenta  acts  in  the  same  way. 

These  dye  salts  continue  to  take  up  the  dye 
with  avidity  to  an  extent  equal  to  four  or  five  times 
the  amount  required  to  coagulate  the  hydroxide. 

No  decomposition  takes  place  here ;  the  dye 
is  absorbed  as  a  whole,  not  as  a  sulphonic  acid. 

Similar  results  we  :e  obtained  with  Methyl  Violet 
and  arsenious  sulphide.  These  absorption  results 
are^confined  to  the  class  of  dye  originally  taken  up. 
The  action  here  is  therefore  of  a  different  nature 
from  that  by  which  basic  dyes  are  held  by  a  direct 
dye  already  present  in  a  fibre. 

It  will  be  remembered  that  similar  absorption 
results  were  obtained  with  tannic  acid  lakes. 

The  evidence  here  is,  therefore,  that  the  original 
action  by  which  the  two  hydrosols  are  coagulated 
is  of  a  chemical  nature.  This  practically  exhausts 
itself  before  the  colour  absorption  stage  commences  ; 
and  this  is  of  a  physical  rather  than  of  a  chemical 
character ,  in  the  case  of  the  mutual  attraction  be- 
tween the  dye  and  the  coagulum.  These  results  led 
Linder  and  Picton  to  support  the  writer's  de- 
solution  theory  rather  than  Witt's  hypothesis  of 
solid  solution.  They  further  consider  that  the 
action  itself  is  of  an  electrical  character  depending 
on  the  properties  of  the  reacting  units,  by  reason 


280         CHEMISTRY  AND  PHYSICS  OF  DYEING 

of  which  two  oppositely  charged  hydrosols  in  strong 
aqueous  solution  seem  to  be  mutual  coagulants. 

The  fibre  substance  is  of  course  already  present 
in  the  insoluble  state,  and  when  in  a  hydrated 
condition  may  possibly  be  taken  as  equivalent  to 
the  coagula  of  the  above  experiments. 

It  must  not  be  taken  for  granted  in  the  present 
state  of  our  knowledge  that  the  dyes  are  always 
precipitated  in  the  fibre  by  direct  attraction.  To 
do  this  it  would  be  necessary  to  ignore  the  phenomena 
of  surface  concentration,  which  is  particularly 
marked  in  the  case  of  pseudo-solutions.  This  may, 
of  course,  be  an  electrical  phenomenon.  It  will  be 
realised  that  the  influence  of  these  general  actions 
in  the  case  of  colloids  cannot  fail  to  be  of  value  to 
the  dyer  in  the  art  of  dyeing  and  printing.  These 
reactions  also  explain  much  that  is  obscure  in  the 
formation  of  lakes  within  the  fibres,  as  in  the  case 
of  alizarine  colours  ;  or  in  their  direct  production  for 
industrial  purposes. 

They  may  equally  modify  our  ideas  on  tanning, 
and  the  manufacture  of  leather. 


CHAPTER  XI 

THE  ACTION  OF  LIGHT  ON  DYEING  OPERATIONS, 
AND  DYED  FABRICS 

THERE  seems  to  be  evidence  that  the  presence  of 
light  may  materially  alter  the  dyeing  results 
obtained  in  some  cases.  The  action  of  light  in 
causing  the  fading  of  dyes  present  on  the  fibres  is 
also  a  very  important  one  to  the  dyer. 

The  action  of  light  on  organic  compounds  in 
general  is  but  little  understood.  Our  knowledge  of 
this  subject  is  incomplete,  but  it  is  already  clear 
that  the  further  study  of  it  will  bring  forward 
many  interesting  facts  for  the  consideration  of  the 
dyer.  The  list  of  substances  which  may  be  altered 
by  the  direct  action  of  light  under  certain  conditions 
is  an  extensive  one.  This  has  long  been  known 
to  those  specially  interested  in  this  subject  from 
a  light  recording,  or  photographic  point  of  view. 

The  action  of  light  has  been  divided  into  two 
classes,  viz.,  Photo-chemical  and  Photo-physical. 

The  division  is  perhaps  an  arbitrary  one,  but 
in  the  first  case  it  is  assumed  that  a  direct  action 
takes  place  which  involves  re-arrangement  in  the 
molecule  itself.  In  the  second  case,  the  action  is 


282         CHEMISTRY   AND   PHYSICS   OF   DYEING 

said  to  be  equivalent  to,  say,  the  polymerisation 
of  formaldehyde. 

Marckwald,  in  attempting  to  explain  the  action 
which  takes  place  in  cases  where  the  alteration 
is  followed  by  a  reverse  action  in  the  dark, 
considers  that  the  actions  which  take  place  in  this 
case  are  not  to  be  explained  by  either  of  these 
causes.  To  the  above  classes  he  therefore  adds  a 
third,  and  suggests  that  this  special  reversible  action 
shall  be  termed  photo-tropical.  Examples  of  this 
are  seen  when]  light  acts  as  quinoquinoline,  or 
t  etrachlor-/3-ket  onaphthalene . 

In  comparing "_;  the  action  of  light  on  organic 
compounds  we  can  either  estimate  the  change  which 
takes  place  in  colour,  or  in  the  absence  of  this, 
by  some  direct  chemical  change  which  is  brought 
about  by  the  action  itself.  The  latter  method  is 
of  course  of  a  more  direct  and  satisfactory  nature 
than  the  former,  in  most  cases,  although  variations 
in  colour  are  valuable  indications  that  some  change 
is  in  progress. 

As  an  introduction  to  the  study  of  this  subject 
the  following  researches  on  the  general  action  of 
light  on  organic  substances  are  of  interest.  They 
indicate  the  possible  nature  of  these  reactions  in  the 
case  of  dyes. 

For  example,  Ciamician  and  Silber  have  con- 
clusively shown  that  this  action  may  give  rise  to 
chemical  change.  Benzophenone  dissolved  in  alco- 
hol is  reduced  to  benzpinacone  and  aldehyde. 
Under  the  same  influence  the  aromatic  orthonitro- 


ACTION  OF  LIGHT  ON   DYEING  OPERATIONS     283 

benzaldehyde    is    transformed     into    nitrosobenzoic 
acid.     The  action  is  indicated  as  follows  : 

CHO       f  „    XOOH 
°    4^ 


Here  we  have  an  action  which  leads  to  the 
internal  re-arrangement  of  the  molecule  rather 
than  to  decomposition. 

Sachs  and  Kempf  (Ber.  1902,  2707)  have  also 
shown  that  a  similar  change  takes  place  with  the 
aniline  compound  of  orthonitrobenzaldehyde.  As 
a  result  of  the  action  nitrobenzanilide  is  produced 
as  follows  : 

„      CH:NC,;H5  CO.NH.QH5 


The  conclusion  arrived  at  is  that  all  aromatic 
compounds  containing  nitro  groups  in  the  ortho 
position  are  sensitive  to  light. 

From  a  general  point  of  view  this  is  of  interest, 
the  action  of  the  light  being  sufficient  to  induce 
intra-molecular  change  or  migration  when  the  side 
groups  are  in  close  proximity  (the  ortho  position). 
The  mordanting  power  of  ortho-hydroxy  compounds 
probably  depends  in  the  same  way  on  the  proximity 

_  Q    TT 

and  combined  action   of   the  _  Q  H   groups,   as    has 

been  noticed  elsewhere. 

When  the  action  of  light  is  accompanied  by 
colour  change,  as  it  is  in  many  cases,  the  actions 
of  this  class  are  classified  under  the  term  chromo- 
tropy.  This  phenomenon  is  very  clearly  shown 


284         CHEMISTRY  AND  PHYSICS  OF  DYEING 

by  the  various  substitution  -  products  of  buta- 
dienedicarboxylic  acid;  for  instance  of 

H,C  =  C  -  CO. 

>0 
H2C  =  C  -  CO/ 

These  compounds  are  all  coloured.  They  are  red, 
brown,  violet,  or  yellow,  as  the  case  may  be. 

These  compounds  undergo  more  or  less  rapid 
change  under  the  influence  of  light.  The  ultimate 
effect  of  this  change  varies  in  its  nature ;  it  is  some- 
times permanent  and  sometimes  temporary. 

The  triphenyl  derivative,  when  exposed  to  the 
direct  action  of  sunlight  for  a  few  minutes,  changes 
its  colour  to  blood -red.  Its  original  colour  is, 
however,  slowly  recovered  in  the  dark. 

If,  however,  the  first  exposure  is  greatly  pro- 
longed, and  extends  for  several  days,  or  even  months, 
the  change  is  of  too  profound  a  nature  for  any  subse- 
quent reversal  of  the  action,  with  regeneration  of 
the  original  form,  to  take  place. 

In  this  case  the  final  products  of  the  action 
seem  to  be  two  white  aldehydes,  with  different 
melting-points,  but  with  the  same  composition,  and 
molecular  weight  as  the  original  substance. 

The  yellow  diphenyl  derivative  yields  three 
distinct  and  colourless  aldehydes  with  different 
melting-points. 

It  is  not  to  be  supposed,  however,  that  the 
products  of  the  action  of  light  are  always  colourless. 
The  dark  red  piperonyl  derivative  yields  two  new 
aldehydes,  which  possess  great  tinctorial  properties. 


ACTION  OF  LIGHT  ON   DYEING  OPERATIONS     285 

These  results  indicate  that  our  present  view  of 
chromophores  must  be  widened  (Stobbe,  Chem. 
Zeit.  1904,  919). 

The  conversion  of  anthracene  into  dianthracene 
under  the  influence  of  light  is  a  reversible  one.  The 
exact  conditions  of  this  change  have  been  'examined 
by  Weigert  (Chem.  Zeit.  1904,  923),  and  Luther  and 
Weigert  (Zeit.  Phys.  Chem.  1905,  53,385),  who  have 
found  that  under  definite  conditions,  and  with  dilute 
solutions  true  equilibria  are  established.  The  source 
of  light  in  the  case  of  these  experiments  was  the  elec- 
tric arc.  As  a  result  of  this  investigation  it  was  found 
that  the  amount  of  dianthracene  formed  depended  on  : 

(1)  The  character  of  the  light. 

(2)  The     change    is    proportional    to    the    light 
intensity,  and  the  surface  exposed,  or  to  the   radius 
of  the  cylindrical  vessels  used. 

(3)  The  action  is  independent  of    the  thickness 
of  the  layer  through  which  the  light  passes. 

(4)  The  action  is  !  inversely  proportional  to  the 
volume   of   the   solution,    and    independent   of   the 
amount  of  anthracene  in  solution. 

Both  the  temperature  and  the  nature  of  the 
solvent  have  an  influence  on  the  result,  and  are 
important  factors  in  determining  the  equilibrium. 

As  is  well  known,  the  leuco  bases  of  many  organic 
substances  are  readily  oxidisable.  Others  are  rela- 
tively stable.  The  action  of  light  seems  to  influence 
these  results.  If  these  substances  are  embedded 
in  collodion  their  sensitiveness  is  greatly  increased. 

This  is  said  to  be  due  to  the  combined    nitric 


286         CHEMISTRY   AND   PHYSICS   OF  DYEING 

acid  affording  an  additional  supply  of  oxygen  under 
the  influence  of  light.  The  fact  has  been  noticed 
also  that  an  addition  of  quinoline  to  the  collodion 
greatly  increases  the  sensitiveness  to  light.  We 
have  here,  therefore,  a  second,  or  foreign,  substance 
influencing  the  reaction  (Konig.  Chem.  Zeit.  1904, 
922). 

In  these  actions  it  has  been  noticed  that  the 
greatest  effect  is  produced  by  complementary  light. 
This  result  seems  to  be  a  general  one,  as  noticed 
later  on. 

A  very  decided  colour-change  which  is  brought 
about  only  in  the  presence  of  a  third  substance, 
which  happens  in  this  case  to  be  a  textile  fibre, 
is  seen  in  the  following  instance.  When  cotton 
yarn  is  padded  with  a  5  per  cent,  solution  of  meta- 
tungstate  of  soda,  and  exposed  to  light,  a  rapid 
change  takes  place  with  the  production  of  a  blue 
colour.  This  is  evidently  due  to  the  reduction  of 
the  salt.  The  action  is  seemingly  a  reversible  one, 
for  if  the  yarn  is  subsequently  stored  in  a  dark 
place,  the  blue  shade  is  discharged. 

If  the  blue  fabric,  or  yarn  be  immersed  in  water, 
the  coloured  compound  is  removed  from  the  fibre. 
In  this  state,  and  away  from  the  influence  of  the 
fibre  substance  it  gradually  resumes  its  colourless 
form,  even  under  the  influence  of  strong  light. 
It  would  seem,  therefore,  that  the  presence  of  the 
fibre  substance  is  the  modifying  factor  in  this 
reaction. 

Turning  to  the  action  of  dyes  themselves  under 


ACTION   OF   LIGHT  ON   DYEING  OPERATIONS     287 

the  disturbing  action  of  light,  the  following  facts 
have  been  noticed.  The  constitution  of  the  dye 
has  a  great  influence  on  the  "  fastness  "  of  the  dye 
against  light.  An  elaborate  series  of  direct  trials 
have  been  made  by  Brownalie  (J.S.D.  and  C.  1902, 
296)  and  as  a  result  the  following  tabulated  con- 
clusions have  been  arrived  at. 

(1)  The  diphenyl  base  plays  little,  or  no  part  in 
the  action. 

(2)  Colours    derived  from  phenol,  or  its  homo- 
logues,  and  their  sulphonic,  or  carboxylic  acids  are 
fast  to  light. 

(3)  Colours   derived  from  hydroxybenzenes  and 
homologues    containing    more    than    one    hydroxyl 
group  are  fugitive. 

(4)  Colours    derived    from    the    amines    of    the 
benzene    series,  and  their   sulphonic   acids,   or  car- 
boxylic acids  are  fugitive. 

(5)  Colours  derived  from  alpha  and  beta  naph- 
thols,  and  their  sulphonic  acids  are  not  fast  to  light. 

(6)  Colours  from  alpha  and  beta  naphthylamines, 
and  their  sulphonic  acids  are  fugitive. 

(7)  Those  from  amido  naphthols,  and  their  sul- 
phonic acids  vary.     The   2.6.8  monosulphonic  acid,, 
and   the    2.3.6.8    disulphonic    acids    are    fast.     The 
1.8.3.6,  and  1.8.2.4  acids  are  fugitive  colours. 

(8)  The  colours  from  the  dihydroxynaphthalenes,. 
and    their   sulphonic   acids   agree   closely  with   the 
corresponding  amidonaphthols. 

(9)  Replacing  amido  by  hydroxyl  groups  results 
in  increased  fastness. 


288          CHEMISTRY  AND  PHYSICS  OF  DYEING 

(10)  The  salt-forming  groups  SO3H  and  CO. OH 
cause  no  difference  in  fastness.  The  auxochromic 
NH2  and  OH  groups  play  important  parts  in  the 
action. 

In  the  case  of  mixed  colours  the  same  rules  are 
followed.  If  the  two  separate  constituents  are  fast, 
so  is  the  dye.  This  is  very  well  seen  in  the  case  of 
the  direct  colour  Diamine  Fast  Red  F,  the  com- 
position of  which  is 

-p       . ,.     ^Salicylic  acid 

^Amidonaphtholsulphonic  acid. 

If,  on  the  other  hand,  both  are  loose,  the  dye  itself 
will  be  an  unsatisfactory  one  in  this  respect.  Delta- 
purpurine  56  is  given  as  an  example. 

Benzidine^3  naphthylaminesulphonic  acid  2.6 
^3  naphthylaminesulphonic  acid  2.7 

In  mixed  dyes,  that  is  to  say,  where  one  of  the 
constituents  is  fast  and  the  other  loose,  the  dye 
generally  stands  midway  between  the  two  in  the 
scale  of  fastness,  but  there  are  many  exceptions  to 
this  rule. 

Three  theories  have  been  put  forward  to  explain 
the  cause  of  this  action.  They  are  of  an  indirect 
nature,  and  may  be  briefly  summarised  as  follows  : 

(i)  The  oxygen  theory. — The  dyes  under  the 
influence  of  light  interact  with  oxygen,  and  form 
colourless  compounds. 

Berthollet  in  1792  came  to  the  conclusion  that 
oxygen  combined  with  the  colours,  and  made  them 
pale. 


ACTION  OF  LIGHT  ON  DYEING  OPERATIONS     289 

The  colour  at  the  end  of  the  exposure  is,  from 
this  point  of  view,  proportional  to  the  resistance 
to  this  action. 

(2)  The  ozone  theory. — The  colours   are   decom- 
posed   or   altered   by  the   production  of  ozone  (or 
hydrogen  peroxide)  in  the  fibre,  chiefly  by  evaporation 
of  moisture. 

(3)  Reduction    theory. — The    dye    is    reduced    by 
cotton  fibre,  or  directly  by  the  action  of  light. 

Experiments  conducted  in  the  presence  of  oxi- 
dising agents  have  given  conflicting  results.  The 
presence  of  sodium  hydrosulphite  solution  also  gives 
varying  results. 

Whatever  be  the  cause  of  the  results  obtained 
in  the  presence  of  oxidising,  or  reducing  reagents,  it 
is  important  to  note  that  dyed  fabrics  always  show 
an  increased  fastness  against  the  action  of  light  in 
vacuo.  This  effect  is  very  marked. 

Similar  experiments  with  sensitive  organic  com- 
pounds are  wanting.  They  should  be  of  equal 
interest. 

A  typical  example  of  this  action  may  be  seen 
when  cotton  dyed  with  Diamine  Sky  Blue  B  is  placed 
in  long  glass  tubes,  which  are  subsequently  exhausted 
by  water  suction  to  a  pressure  of  10  mm.  (9  mm.  of 
which  are  due  to  water  vapour),  and  exposed  for 
fourteen  days  to  bright  light.  The  shade  remained 
absolutely  unchanged.  A  comparison  trial,  which 
was  exposed  to  the  light  side  by  side  with  the  other 
one,  but  under  ordinary  conditions,  had  entirely 
lost  its  colour.  The  cotton  was  quite  white- 


2QO          CHEMISTRY  AND  PHYSICS  OF  DYEING 

The  same  blue  cotton  sealed  in  a  tube  in  an 
atmosphere,  of  oxygen  gas  lost  its  colour  even  more 
rapidly  than  the  above  comparison  sample.  On 
the  other  hand,  the  colour  remained  unaltered  in 
an  atmosphere  of  either  hydrogen,  carbon  dioxide, 
sulphur  dioxide,  or  coal  gas.  When  exposed  in 
nitrous  oxide  gas  the  effect  produced  was  very 
similar  to  that  noticed  in  the  case  of  oxygen. 

It  is  evident,  therefore,  that  dyed  samples  in  the 
absence  of  oxygen  will  not  fade. 

Berthollet  in  1792  noticed  that  the  fading  action 
of  colours  seemed  to  be  intensified  in  the  presence 
of  an  alkali.  In  the  same  way  an  acid  condition 
seems  to  retard  the  fading  action. 

The  fact  that  the  fading  is  intimately  connected 
with  the  presence  of  oxygen  may,  therefore,  be  taken 
as  established.  It  remains  to  trace  the  actual 
action  which  takes  place.  It  has  been  noticed  that 
the  evaporation  of  water  at  ordinary  temperatures 
leads  to  the  formation  of  ozone  in  very  small 
quantities. 

The  fading  of  the  colours  may,  therefore,  be 
due  to  the  direct  interaction  between  the  ozone,  or 
hydrogen  peroxide  so  formed,  from  the  oxygen 
in  the  air ;  colourless  compounds  of  unknown 
composition  being  produced.  The  action  seems  also 
to  be  proportional  to  the  moisture  present  at  the 
time  of  the  experiment. 

Under  the  influence  of  the  light  vibrations  the 
oxygen  molecule  may  be  more  readily  split  up,  and 
an  action  of  the  following  order  induced  : 


ACTION  OF  LIGHT  ON   DYEING   OPERATIONS     291 

02   ^   O  +  O 

and   this   may   take  place   more   readily  when   the 
oxygen  is  associated  with  water  molecules. 

Whatever  the  action,  the  result  is  clearly  seen 
in  the  alteration  in  colour. 

The  most  favourable  atmosphere  for  this  lading 
action  is  a  hot,  moist,  and  alkaline  one. 

It  has  also  been  noticed  that  the  presence 
of  such  seemingly  inert  substances  as  alcohol 
and  pyridine  vapour  will  greatly  influence  the 
rate  of  fading.  It  is  greatly  accelerated  in  their 
presence. 

Although  our  knowledge  is  incomplete,  we  may 
at  least  assume  that  the  action  is  a  very  com- 
plicated one,  and  beyond  recording  certain  facts, 
we  are  confined  to  most  indefinite  speculations. 

The  influence  of  the  fibre  is  also  a  factor  to  be 
considered.  All  fibres  do  not  act  in  the  same  way. 
The  fastness  of  the  same  dye  varies  on  different 
fibres.  Methylene  b]ue  on  cotton  is  faster  than  on 
wool.  Indigo  on  the  other  hand  gives  more 
fugitive  shades  on  wool  than  on  cotton. 

Colours  dyed  on  cotton,  oxycellulose,  trinitro- 
cellulose  and  jute  are  said  to  be  all  equally  fast. 
This  might  be  put  forward  as  an  argument  that 
there  is  no  chemical  action  in  dyeing  these  fibres, 
the  dye  being  present  in  all  cases  in  the  same  state. 
On  silk  eighty-four  per  cent,  of  the  colours  experi- 
mented with  showed  no  difference  ;  sixteen  per  cent, 
were  said  to  be  slightly  faster. 


292          CHEMISTRY  AND  PHYSICS  OF  DYEING 

There  are  therefore  three  factors,  at  least,  which 
may,  under  these  same  conditions,  influence  the  rate 
of  fading,  viz.,  the  physical  condition  of  the  dye  in 
the  fibre,  that  is  to  say,  its  state  of  division  ;  the 
possibility  of  some  chemical  action  between  the 
fibre  and  dye,  and  the  transparency  of  the  fibre 
substance  in  its  relation  to  the  passage  of  the  light 
rays. 

The  statement  that  cotton  colours  are  fast  in 
solution,  but  not  on  the  fibre,  is  not  correct. 

The  general  conclusion  arrived  at,  therefore,  in 
the  present  state  of  our  knowledge,  is  that  the 
action  is  an  oxidising,  and  not  a  reducing  one.  In 
the  absence  of  oxygen  there  is  no  change  in  colour, 
due  to  the  direct  action  of  light.  The  action  is  also 
proportional  to  the  moisture  present  on  the  fibre. 
It  is  clear  also  that  the  constitution  of  a  colour 
determines  its  stability. 

An  advance  in  our  knowledge  of  this  subject 
was  made  by  Depierre  and  Clouet  (J.S.D. 
and  C.  1885,  245),  when  these  authors  discovered 
that  the  action  of  light  depended  upon  its 
nature.  It  might  be  expected  that  the  so-called 
chemical  rays  would  have  a  greater  efficiency  in 
this  action  in  the  same  way  that  they  have  a 
greater  influence  in  the  decomposition  of  photo- 
chemical salts.  As  a  matter  of  fact,  this  is  not  the 
case.  It  must,  however,  be  remembered  that  we 
have  here  a  disturbing  action  in  the  case  of  dyes, 
due  to  colour-filtering  effect.  This  natural  screen 
may  therefore  in  its  action  veil,  or  modify,  the 


ACTION  OF  LIGHT  ON  DYEING  OPERATIONS     293 

original  effects  of  the  light.  The  most  active  rays 
may  only  have  a  chance  of  acting  superficially  in 
some  cases,  at  any  rate,  and,  therefore,  have  their 
normal  action  incidentally  modified.  Less  active 
rays  which  are  passed  on  through  the  superficial 
screen  may  actually  have  a  greater  cumulative 
effect. 

Dufton  (J.S.D.  and  C.  1894,  p.  92)  has  shown 
that  in  any  case  the  waves  which  are  most  readily 
absorbed  are  the  most  active  ones.  That  is  to  say, 
the  colours  complementary  to  those  reflected  pro- 
duce the  greatest  effect.  This  seems  to  be  a 
general  law.  The  absorption  of  rays  may,  as  in 
the  cases  given  at  the  beginning  of  this  chapter, 
produce  a  state  of  strain  in  the  dye  molecule  leading 
to  a  different  state  of  equilibrium,  or  formation  of 
fresh  compounds,  and  apart  from  this  the  formation 
of  active  "  oxygen "  compounds  would  seem  to 
bring  about  the  change  in  the  dye  which  leads  to  the 
change  in  colour.  Assuming  the  quinonoid  theory 
of  colour,  it  would  be  necessary  to  allow  that  the 
structure  of  the  dye  molecule  is  profoundly 
modified. 

The  whole  subject  is  of  extreme  importance  to 
the  dyer,  and  should  receive  more  attention. 

For  instance,  it  has  been  generally  allowed  that 
the  basic  colours  produced  on  an  antimony  tannin 
lake  are  fast  as  compared  with  those  on  tannic 
acid  itself.  This  action  is  an  obscure  one,  and 
hardly  agrees  with  the  contention  that  dyes  in  the 
presence  of  acids  are  faster  against  light. 


294          CHEMISTRY  AND  PHYSICS  OF  DYEING 

It  has  been  stated  elsewhere  that  the  action  of 
light  is  an  important  factor  in  the  dyeing  of  Turkey 
Red  on  cotton. 

Another  case  of  the  influence  of  light  in  the 
process  of  dyeing  is  that  noticed  by  Pokorng 
(Bull.  Soc.  Ind.  Mulh.  1893,  282).  Wool  and  silk 
"  dyed "  with  naphthylamine  become  darker  in 
shade  on  exposure  to  light.  The  shades  produced 
by  subsequent  treatment  with  nitrous  acid  are  also 
much  darker  than  those  from  the  original  skein. 
The  action  of  light  on  diazotised  primuline  or  silk 
has  even  been  made  the  basis  of  a  photographic 
process  by  Messrs.  Green,  Cross  and  Bevan  and 
Farrell  respectively. 

There  is  clearly  plenty  of  scope  for  further  re- 
search on  this  interesting  and  almost  untouched 
branch  of  the  subject. 

The  action  of  light  on  the  natural  colouring- 
matters  present  in  the  vegetable  fibres  is  well  known. 
It  is  taken  advantage  of  in  the  bleaching  of  linen, 
and  was  at  one  time  universally  used  for  this  purpose. 

In  the  case  of  cotton  the  action  is  greatly  in- 
creased if  the  fibre  is  previously  treated  with  a 
soda  dye-bath.  Such  a  sample  will  be  well  bleached 
before  the  other  one  is  appreciably  lightened  in 
colour,  under  the  same  conditions. 

The  fact  has  been  recorded  that  some  dyes  in 
solution  will  dye  the  glass  containing  vessel  to  a  far 
greater  extent  on  the  side  which  faces  the  light. 
This  is  possibly  due  to  the  more  solvent  action  of 
the  water  on  the  glass  in  the  presence  of  light,  or 


ACTION  OF  LIGHT  ON  DYEING  OPERATIONS     295 

even  to  its  decomposition,  rather  than  any  action 
in  the  dye  itself.  The  action  seems  to  be  a  very 
slow  one. 

To  the  student  this  subject  is  an  absorbing  one. 
It  may  be  attacked  either  from  the  point  of  view 
of  the  fibres,  or  from  that  of  the  reactions  which  take 
place  when  light  acts  on  organic  compounds.  In 
either  case  important  results  must  follow  a  careful 
study  of  the  subject. 

Two  changes  which  take  place  under  the  influ- 
ence of  light  rays,  and  which  are  both  connected 
with  indigo,  are  of  interest. 

The  first  is  that  noticed  by  Kopp  (Bull,  Soc. 
Ind.  de  Mulh).  Kalle's  indigo  salt  is  very  sen- 
sitive to  light  when  present  as  the  bisulphate 
compound.  A  dyeing  process  has  even  been 
founded  on  this  fact.  The  nature  of  the  reaction  is 
unknown. 

The  second  is  that  benzylidineorthonitroaceto- 
phenone  is  converted  into  indigo  by  the  action  of 
light  by  intermolecular  oxidation.  No  action  takes 
place  in  the  dark,  very  little  in  the  red  rays,  more 
in  the  green,  and  the  influence  reaches  a  maximum 
in  the  violet  (Engler  and  Dorant,  Ber.  28,  2497). 
The  inference  is  that  the  action  is  closely  connected 
with  the  presence  of  the  chemical  rays. 

The  student  might  also  refer  to  some  work  done 
by  W.  Straub  (Archiv  fur  Exp.  Path,  und  Pharm. 
51*  383),  on  the  action  of  light  on  eosin  under 
special  circumstances. 

The  complete  decolorisation  of  this  dye  required 


296          CHEMISTRY  AND  PHYSICS  OF  DYEING 

65  molecules  of  oxygen.  The  action  is  ascribed  to 
the  production  of  eosin  peroxide  in  the  case  in 
question. 

It  will  be  remembered  that  the  fastness  of  lakes 
depends  on  the  nature  of  the  "  absorbing"  material. 
Quite  recently  W.  E.  Evans  (Eng.  Pat.  19795,  1905) 
has  shown  that  light  influences  the  drying  of 
materials.  It  is  said  that  the  action  may  either 
hasten,  or  retard  this  operation  according  to  its 
nature. 


CHAPTER  XII 
METHODS  OF  RESEARCH 

IT  is  considered  advisable  for  the  benefit  of  students 
and  others,  who  contemplate  starting  original  work 
on  this  subject  to  outline  briefly  the  methods  used 
by  previous  workers,  so  far  as  they  have  been 
published. 

The  methods  used  are  simple  in  their  nature, 
and  in  many  cases  are  similar  to  those  used  in  the 
practice  of  dyeing. 

Direct  weighing  method. — The  fibre  is  carefully 
weighed  on  a  chemical  balance,  before  and  after, 
the  experiment. 

The  process  is  not,  as  a  rule,  a  satisfactory  one. 
For  instance,  it  has  been  used  to  record  the  actual 
gain  in  weight  of  fibres  which  have  been  mordanted 
under  different  conditions.  The  net  gain  in  weight 
is  registered,  and  this,  perhaps,  in  ordinary  dyeing, 
mordanting,  or  weighting,  experiments  may  be 
satisfactory,  yet  the  actual  nature  of  the  addition 
in  many  cases,  can  be  only  guessed  at,  or  is  even 
unknown. 

This  must  be  determined  by  actual  chemical 
analysis.  This,  in  many  cases,  is  a  very  difficult 


298          CHEMISTRY  AND  PHYSICS  OF  DYEING 

operation,  and  entails  the  elaboration  of  special 
methods. 

It  is  probable  that  in  the  future  such  a  rough 
and  ready  method  of  estimation  will  receive  little 
support  except,  of  course,  in  cases  where  the  re- 
action between  fibre  and  substance  absorbed  can 
be  readily  ascertained,  and  is  beyond  question. 
For  instance,  it  might  be  a  satisfactory  method  of 
showing  the  different  results  obtained  by  the  treat- 
ment of  silk  with  pure  tannic  acid.  On  the  other 
hand,  it  would  be  a  very  unsatisfactory  way  of 
indicating  the  action  of  silk  on  stannic  chloride 
solution,  or  wool  on  bichromate  solution.  Any 
further  experiments  on  the  action  of  mordants,  can 
have  very  little  value,  if  they  are  simply  of  this 
nature.  The  composition  of  the  salt  fixed  must 
be  clearly  determined,  and  any  alteration  in  the 
composition  of  the  mordant  solution  itself, 
noted. 

The  condition  of  the  fibre,  in  these  experiments 
may  have  a  disturbing  effect  on  direct  weighing. 
The  percentage  of  moisture  must  be  estimated,  and 
allowed  for. 

This  method  is  not  satisfactory  in  the  case  of 
dyeing  with  aniline  colours,  unless  they  are  present 
in  large  quantities.  Even  here,  it  is  advisable  to 
check  the  amount  of  dye  left  in  the  solution,  by 
processes  mentioned  further  on  in  this  chapter. 

Much  of  the  present  uncertainty  of  the  reactions 
in  dyeing,  is  clearly  due  to  the  primitive  nature  of 
many  of  the  recorded  experiments.  Such  a  state  of 


METHODS  OF  RESEARCH  299 

affairs  would  not  be  tolerated  in  any  other  branch 
of  chemical  or  physical  work. 

The  conditions  of  the  fibre  state  must  not  be 
allowed  to  vary  without  record.  Perhaps  the  most 
difficult  problem  in  connection  with  such  work  is 
the  standardising  of  a  fibre  state,  which  shall  be 
constant  and  easily  reproduced  at  will.  Such  treat- 
ment as  is  generally  adopted  in  practice,  which  may 
entail  the  use  of  solutions  of  acid  or  alkaline 
reaction,  is  of  a  doubtful  nature. 

The  action  of  such  reagents  is  disturbing  and 
specific  and,  with  our  present  knowledge,  it  is  im- 
possible to  estimate  their  influence  on  the  fibres, 
with  any  certainty,  or  indicate  their  effect  on  the 
absorption  values. 

Ultimate  analysis. — This  is  only  satisfactory  in 
rare  instances,  for  the  reasons  which  hold  in  the 
above  case. 

It  may  be  used  to  estimate  the  percentage  of 
nitrogen  in  silk.  The  percentage  present  in  the 
fibre  is  17.6.  The  greatest  care  must,  however,  be 
taken  to  exclude  the  possibility  of  any  other  nitro- 
genous substances  being  present,  and  so  interfering 
with  the  result. 

Persoz  (Monit.  Sclent.  1887,  597)  suggests  that 
silk  be  reduced  to  a  powder  after  treatment  with 
30  per  cent,  hydrochloric  acid.  The  nitrogen  factor 
is  then  increased  to  18  per  cent.  The  advantage 
of  this  procedure  is  doubtful. 

Estimation  of  ash. — This  may  be  useful  to  indi- 
cate the  presence  of  mineral  matter  in  the  case  of 


300          CHEMISTRY  AND   PHYSICS  OF  DYEING 

the  absorption  of  inorganic  mordants.  The  com- 
position of  the  ash  should,  however,  be  determined 
and  the  possible  action  of  incineration  on  its  com- 
position allowed  for. 

Direct  analysis. — Wherever  possible  this  method 
should  be  adopted.  For  instance,  if  this  method 
had  been  used  throughout  in  Heermann's  ex- 
perimental work  on  the  action  of  mordants  the 
results  obtained  would  have  been  of  greater 
value. 

The  work  necessary  to  devise  special  methods 
of  analysis  to  meet  the  requirements  of  the  work 
is  often  of  a  tedious  nature.  It  may  even  be  im- 
possible to  devise  such  direct  methods  of  determining 
the  actions  involved,  but  whenever  possible  they 
should  be  used.  The  methods  in  use  for  ordinary 
analysis  are,  of  course,  available. 

Acidimetric  methods  are  useful  to  estimate 
acids,  alkalies,  and  the  absorption  of  these  sub- 
stances by  fibres,  if  special  precautions  are 
taken. 

In  some  cases  acid  colours  may  be  directly 
estimated  by  a  standard  solution  of  Night  Blue. 

In  the  same  way  tannic  acid  is  said  to  give  good 
results  when  used  to  estimate  basic  colours. 

Knecht  has  recently  recommended  the  use  of 
titanium  salts  for  the  volumetric  method  of  esti- 
mating dye-stuffs  insolution(/.S.C.  and  D.  24.  154). 
This  should  be  useful  in  many  cases. 

The  estimation  of  alizarine  and  mordant  colours 
is  a  difficult  operation.  Their  "  mordant  value " 


METHODS  OF  RESEARCH  301 

may  be  obtained  by  the  method  suggested  by  the 
writer  (J.S.C.I.,  12,  997). 

Solvent  action  of  reagents. — This  has  been  used 
to  indicate  the  way  in  which  colours  are  held  by 
fibres. 

This  method  was  adopted  by  the  writer  to 
determine  the  relative  "  fastness  "  of  ingrain  and 
direct  dyed  colours.  Other  cases  will  also  have 
been  noticed  where  this  method  is  made  use  of, 
particularly  where  alcohol  has  been  used  to  extract 
dye  from  the  fibre.  Benzene,  and  amyl  alcohol, 
have  also  been  used  for  this  purpose  with 
success. 

Direct  colour  estimation. — The  numerous  tincto- 
meters  in  vogue  may  be  used  for  this  purpose.  With 
the  Lovibond  instrument  a  direct  colour-record  may 
be  kept  of  any  dye  solution.  It  may  even  be  used 
for  the  estimation  of  dyes  on  fabrics. 

Mills  and  Hamilton  used  the  tinctometer  to 
estimate  the  relative  absorption  of  dyes  by 
fibres. 

This  method  is  a  very  accurate  one  when  the 
amount  of  colour  present  in  a  solution  is  small. 

Estimation  by  dyed  sample. — A  shade  is  matched 
by  direct  dyeing  on  the  same  fibre  under  standard 
conditions.  This  method  is  useful  in  cases  where 
the  dye-bath  is  exhausted. 

Relative  dyeing  properties  of  fibres. — This  may 
sometimes  indicate  changes  like  those  which  take 
place  during  the  mercerising  action,  or  in  the  nitra- 
tion of  cotton  fibre. 


302          CHEMISTRY  AND  PHYSICS  OF  DYEING 

Thermo  chemical  reactions  are  recorded  by  special 
means,  and  involve  the  use  of  a  calorimeter. 

Dissociation  and  association  effects  in  solution. 
-The  student  is  referred  to  the  standard  books 
on  physical  chemistry  for  information  on  this 
subject. 

Temperature. — The  control  of  the  temperature 
during  experiments  in  dyeing  is  often  of  great 
importance.  This  may  be  effected  by  the  use  of 
a  thermostat. 

Spectroscopic  examination. — Formanek  recom- 
mends this  process  of  analysis  for  the  detection 
of  colouring-matters,  particularly  of  the  variations 
in  colour  noticed  after  treatment  with  certain 
reagents,  such  as  ammonia,  nitric  acid,  &c. 

Polarised  light. — Chardonnet  has  used  this 
method  to  distinguish  the  different  states  of  ni- 
tration in  nitrocellulose. 

Hiibner  and  Pope  indicate  that  they  are  using 
this  to  indicate  change  in  the  fibre  state  during 
the  process  of  mercerising. 

To  a  great  extent  the  investigator  must  be  guided 
by  the  problems  before  him,  and  the  general  and 
recognised  methods  of  analysis  should  be  utilised 
wherever  possible  to  the  exclusion  of  such  tests  as 
the  mere  weighing  of  the  fibres  before  and  after 
treatment,  or  comparative  dye  trials. 

The  student  should  make  certain  that  when- 
ever possible  his  work  shall  be  of  a  quantitative 
nature,  and  that  the  conditions  of  the  experiments 
are  accurately  recorded. 


METHODS  OF   RESEARCH  303 

Special  attention  should  be  given  to  reactions 
which  take  new  directions  or  are  modified  in  the 
presence  of  fibres. 

Such  particulars  as  deal  with  the  physical  con- 
stants of  solutions  must  be  sought  for  in  the  recog- 
nised text-books  on  the  subject. 


INDEX  OF  AUTHORS 


ABEGG,  64 
Armstrong,  37,  103 
Appleyard,  25,  175,  188 
Arrhenius,  114 

BANCROFT,  33 

Baeyer,  227 

Bauer,  143 

Behre,  276 

Benedikt,  59 

Bemmelen,  116,  118,  127 

Bentz,  194 

Bergmann,  140,  180 

Berthollet,  5,  140,  183,  288 

Bevan,  see  Cross 

Billitzer,  121,  274 

Biltz,  43,  124,  275,  276 

Binder,  59 

Bing,  259 

Binz,  204,  209,  213,  214,  259 

Bolby,  6 1 

Bourry,  30 

Boettiger,  215 

Brand,  200 

Bretonniere,  47 

Bronnert,  21 

Brown,  100,  269,  272 

Brownalie,  287 

Buntrock,  40 

CAREA  LEA,  63 
Carter,  158 
Chabrie,  267 
Champion,  25 
Chaptal,  5 
Chardonnet,  302 
Chevreul,  5,  61,  140,  183 


Ciamician,  282 

Clouet,  292 

Collingwood,  98 

Coninck,  60 

Cox,  64 

Cramer,  28,  80,  230 

Croissant,  47 

Crompton,  103 

Cross,  15,  21,  79,  172,  173,  262. 

294 
Crum,  142 

D'APLIGNY,   LE   PILEUR,    5,    55, 

140,  183 
De  Girardin,  5 
De  Saussure,  142 
De  Mosenthal,  144,  255 
De  Vitalis,  5 
Depierre,  292 
Donnon,  134 
Dorant,  295 
Dreaper,   18,  39,   104,   113,   152, 

163,   165,   173,   174,   195,  202, 

246,  255 
Duclaux,  123 
Dufay,  181 
Dufton,  293 
Duschak,  180 

ENGLER,  295 
Erdmann,  80 
Esson,  148 
Evans,  296 
Ewer,  214 


FABER,  13 

Far r ell,  194,  294 


20 


306 


INDEX  OF  AUTHORS 


Fischer,  29,  151 
Fischli,  60 
Flick,  30 
Fornianek,  302 
Franklin,  137 
Freudenberger,  137 
Friedemann,  122 

GARDNER,  P.,  19 

Gardner,  W.  M.,  97,  158 

Geiger,  128 

Geigy,  35 

Georgievics,  v.,  34,  40,    46,    62, 

151,    170,    176,    189,  211,  215, 

229,  249,  260 
Gelmo,  77,  91 
Gillet,  93 
Gladstone,  129 
Gmelin,  227,  230 
Gonfreville,  61 
Goppelsroeder,  224 
Gore,  264 
Graham,  109 
Green,  13,  37,  47,  49,  190,  207, 

214,  294 
Guthrie,  129 

HALLITT,  152 

Hamilton,  145,  301 

Hanofsky,  21 

Hantzsch,  227 

Harcourt,  148 

Hartl,  1 80 

Harvey,  62 

Hawkesbee,  250 

Heermann,  67,  300 

Hellot,  4,  140 

Henri,  123,  137 

Hepburn,  201 

Hibbert,  129 

Hirsch,  93,  95,  208,  213,  214 

Hirst,  209 

Hoff,  Vant,  168,  179 

Hollman,  83 

Hood,  147 

Hiibner,  82,  269,  302 

Hulett,  1 80 


Hummel,  62,  187,  232 
Hwass,  146 

JACOBS,  MULLER,  214,  234 
Jannasch,  180 
Jaquemin,  225 
Jones,  49 
Jones,  H.  C.,  103 

KAUFER,  148 

Kempf,  283 

Kilmer,  81 

Klobbie,  116 

Knecht,  25,  26,63,  I3I»  T54>  i$6, 

158,    187,   188,    193,  205,  217, 

249,  300 
Krechlin,  260 
Kohlrausch,  106 
Konig,  286 
Kopp,  295 
Korte,  1 80 

Kostanecki,  v.,  39,  40 
Kraflt,  135,  239 
Kuenen,  133 
Kuhlmann,  185 
Kurz,  201 
Kuster,  177 

LEFEVRE,  19 

Levy,  207 

Liechti,    54,    56.    62,    170,    192, 

232 

Liebermarm,  39 
Liesegang,  124 
Linder,  43,    123,   246,   256,   274 

_278 

Linnebarger,  126 
Lowry,  104 
Lubavin,  128    „ 

MACQUER,  140,  182 
Masson,  22 
Marchlewski,  231 
Marckwald,  51,  282 
Martini,  22 
Matthews,  206 
Mayer,  123,  137,  229, 


INDEX  OF  AUTHORS 


307 


Mendeleef,  103 
Mercei.  17 
Meyenberg,  47 
Mills,  84,  145,  148,  301 
Minajeff,  82 
Moehlau,  40 
Mohlau,  65,  147,  207 
Morris,  129 
Musprat,  185 

NASSO,  128 
Neisser,  122 
Noetling,  40,  59 
Nollet,  113 
Nietzki,  64,  '.08 

ORICELLI,  2 
Ostwald,  1 80 

PALEWSKY,  51 

Paterno,  128 

Pauly,  204 

Payen,  128 

Perkin.  33,  266 

Persoz,  5,  58,  184,  299 

Picton,  123,  135,  239,  246,  274 

Pick,  214 

Pickering,  103 

Plaff,  128 

Pliny,  2 

Pollak,  47 

Pokorng,  147,  167,  257,  258,  294 

Pope,  82,  269,  302 

Pouillet,  22 

Prager,  von,  33,  146,  189,  213 

Prud'homme,  42,  94,  229 

QUINCKE,  266 

RAMSAY,  1 14 
Ramsden,  265 
Rennie,  148 
Richard,  24 
Richards,  180 
Richardson,  27,  230 
Rossi,  201 
Rotheli,  227,  230 


Rouard,  61 

SACHS,  283 

Sabaneeff,  128 

Schafer,  229 

Schaposchnikoff,  82 

Scheurer,  17,  82 

Schmidt,  177 

Schmidner,  151 

Schneider,  179 

Schroeter,  209,  213,  214 

Schultz,  269 

Schumacher,  234 

Schunck,  229,  231 

Schiitzenberger,  61,  230 

Sheppard,  175 

Shields,  129 

Silber,  282 

Silbermann,  151 

Sisley,  51,  167 

Skita,  29 

Steimmig,  40,  65 

Stern,  17 

Stobbe,  ^85 

Storck,  6u 

Straub,  295 

Suida,  20,  21,  54,  56,  77,  91 

Spon,  146,  147 

TAKAMINE,  84 
Tauss,  80 
Thenard,  61 
Thompson,  143 
Thomson,  262 
Tollens,  13 
Tomasso,  127 
Tompkins,  18 
Trantmann,  42 
Tyndall,  135 

ULRICKS,  189 
Ulzer,  59 

VANINO,  180 
Veley,  129 
Vergnaud,  5 
Verguin,  33 


308 

Vidal,  47 

Vignon,  95,   130,  207,  220,  224, 

249 
Voigtlander,  112 

WALKER,  137,  175,  252 

Washburn,  77 

Weber,   132,   138,  149,  173,  175, 

230,  240,  262 
Weigert,  285 


INDEX  OF  AUTHORS 
Weil,  227 


Werner,  258 
Wilhelm,  132 
Willstatter,  207 
Wilson,  163 

Witt,  34,  66,  1 68,  173,  243,  279 

YEOMAN,  49 
ZACHARIAS,  150 


INDEX 


ABSORPTION,  42,  44,  86,  1 17,  1 18, 
124,  1 60, 171, 177, 179, 1 80, 
197,  207,  234,  276,  279 
causing    decomposition,    24 
compounds,  44,  279 
strength  of,  solution  on,  44, 

171,  179,  234 
maximum,  188,  261 
of  organic  substances,  221 
Absorptive  power  of  silk,  85 
cotton,  87 
wool,  85 

Acids.,  action  of,  84,  162,  167 
in  dyeing,  89,  149,  154 
basic  colours 
acid    colours,    93,    154, 

191 

Acid  salts,  18 
Adjective  colours,  33 
Aggregates,  size  of,  251,  254 
Alanine,  28,  29 

phenyl,  3,  29 
Albumen,    action    of,    128,    192, 

244 

Albumenoids,  reactions  of,  83 
Alcohol,  action  of,  213,  227,  272 
Alkalies,  action  of,  95,  261 

absorption  by  fibres,  87 
Aluminium  chloride,  21 

salts,  54,  59 
Alizarates,  49,  61 

solution  in  alcohol-ether,  60 
Alizarines,  38,  43,  45,  56 

quinoid  form  of,  lakes,  45 
Alkylated  diazo  dyes,  229 
Alum,  61,  183 
Amido  acids,  25 


Amido  acids,  theory  of,  25,  186, 

206 

Amidoazobenzenes,  210,  238 
Amidoglyceric  acid,  28 
Amido  groups,  35,  36,  39 
Amine  dyes,  195,  211 
Amines,  absorption  of,   147,  257 
Ammonium  sulphate,  action  of, 
128 

acetate,  215 

Amorphous  substances,  109 
Amyl  alcohol,  169 
Aniline,  black,  48 

yellow,  238 

Antimony  mordants,  67 
Animalising  fibres,  224 
Arganine,  29 

Aromatic    acids,    absorption   of, 
179 

oxy derivatives,  30 

phenols,  159 

Arsenious  sulphide,  247,  251,  256 
Artificial  fibre  substance,  228,  275 

membranes,  235 
Asbestos,  dyeing  of,  147 
Assistants,  action  of,  64 
Association  theory,  103 
Atomic  migration,  255 
Atropine  hydrochloride,  207 
Auxochromes,  35 
Azobenzenecarboxylic  acid,  211 
Azo  dyes,  35,  212 
Azo  triple  dyes,  196 

BARIUM  chloride,  action  of,  180, 

271 
salts,  dyeing  with,  149,  230 


3io 


INDEX 


Basic  colours,  34,  48,  91,  242 

action  of  light  on,  240,  241, 

246 
decomposition  of,  93,  187, 

226,  241,  250 
dyeing  with,  91,  93,  99 
lakes  of,  48,  244 
Benzidine  salts,  207,  209 
Benzoic  acid,  178 
Berberine  hydrochloric! e,  145 
Bleaching,  82 
cotton,  82 
silk,  75 
wool,  78 
"  Boil  off  "  liquor,  75 

standard,  76 
Borax,  action  of,  74 
Bronzing  effect,  168,  170 

CACHOU  de  Laval,  47 

Calcium  salts,  influence  of,  45,  56, 

58,  65,  81 
Calico-printing,  5 
Capillary  action,  142,  144,  250 
Carboxyl  groups,  38 
Casein,  237 
Cellulose,  12,  79 

action  of    reagents  on,    12, 
15,  18,  20,  224 

acyl  derivatives,  20 

alkyl  derivatives,  20 

catalysing  action  of,  2 1 

constitution  of,  13 

regenerated,  13 

thiocarbonate,  13 
Centrifugal  action,  influence  of. 

137 
Chemical  action,   147,   154,   180, 

192,  208,  222,  225 
Chemical    theory    of    dyeing,    7, 

1 80,  1 86 

Chromate  of  chromium,  64 
Chromium  mordants,  43,  63,  65 
Chromogens,  34 
Chromophores,  34,  42 
Chrysoidine,  238 
Classification  of  dyes,  33,  236 


Coagulation,  an  electrical  effect, 

280 

Cochineal,  2 

Colloid  theory  of  dyeing,  234 
Colloids,  9,  102,  107,  239 

absorptive    power    of,    115, 

276 
action   of    barium   sulphate 

on,  126,  176,  180 
action  of  electrolytes  on,  127 
carrying    down     power    of, 

120 
classification    of,    122,    125, 

138 

dehydration  of,  126 
diffusion  of,  112,  135 
electrically  charged,  122 
hydration  of,  127 
inorganic,  absorption  of,  124, 

i 86,  276 

molecular  weight  of,  125 
power  of  coagulating,    122, 

127 
precipitation     of     insoluble 

salts,  124 
reactions  of,    116,    120,    128, 

248,  274 
separation     by     centrifugal 

force,  137 
freezing,  128 
water  in,  126 
Colloidal  silica,  127 
Colour  acids,  90,  132,  156,  191 
Colour  of  dyed  fabrics,  200 

sensibility,  175 
Complementary  light,  286 
Condensation  theory  of  dyeing, 

212 

Congo  Red,  46,  215 
Constitution  of  dyes,  34 

influence  on  fastness,  287 
Copper  mordants,  45,  65 
Cotton,  12,  142 
acid  salts,  18 
acids  on,  16,  84 
alkalis,  18,  79 
reagents  on,  8 1 ,  1 84 


INDEX 


Cotton  dyes,  46,  135 

mercerised,  18 

mordants  on,  54 

nitrated,  16,  20 

preliminary     treatment    of, 
230 

solutions  of,  12,  17 
Coupling  dyes,  218 
Crystalloids,  109 

DEAMIDATED  fibres,  194 
Degraded  solutions,  265 
Dehydration  of  colloids,  127,  157 
Dehydrotheotoluidine    sulphonic 

acid,  190 
De-solution,  104,  246,  251,  272 

by  capillary  action,  268 

cause  of,  207 
Developed  dyes,  202 
Developers,  action  of,  196 
Diamine  colours,  39,  131 ,206,  2 1 8 
Diamino  acids,  29 
Dianisidine  hydrochloride,  207 
Diazobenzene,  209 
Diazo  reaction  with  silk,  29 

wool,  200 
Diazotised  fibres,  29,  193 

primuline,  190 
Diazoxylene,  209 
Diffusion,  112 

through     membranes,     112, 
236 

of  colloids,  112,  135 

of  dyes,  135,  136 
Dinitrodiazoamidobenzene,  201 
Dye  in  free  state,  149,  230 
Dyes,  32,  34 

acid,  34 

action  of  /3  rays  on,  137 

basic,  34 

classification  of,  33,  236 

constitution  of,  34,  36 

dissociation  of,  130,  150 

identification  of,  49 

influence  of  constitution  on 
shade,  37 

solubility  of,r5o,  122,  151 


Dyes,  solution  state  of,  1 36 

vegetable  dyes,  32 
Dyeing,    57,   94,    131,    140,    165, 

214,  270 
cause  of,  211 
cotton,  82,  99,  169,  200 

and  silk,  215 
conditions  of,  72,   197,  204, 

260 

deamidated  fibre,  206 
inert  substances,    226,    232, 

240 

inorganic  colloids,  277,  278 
in  alcohol,  167,  178 
in  alcohol-ether,  60,  133 
in  benzene,  132,  178 
in    different    solvents,    132, 

167 
in     molecular     proportions, 

189 

in  neutral  solutions,  91 
ingrain  colours,  173,  195,  200 
jute,  12 

part  played  by  water,  258 
with  acid  colours,  93,  192 
with  mixed  colours,  145 
with  nitro  colours,  208 
wool,  91,  145 
Dyewoods,  2 

EBULLIOSCOPE,  240 
Electrical  dissociation,  51 
Endosmosis,  263 
Exosmosis,  263 
Exothermic  reaction,  22 

FARADAY'S  LAW,  106 
Fastness  of  colours,  241,  287 
Fibres,  n 

action  on  mordants,    56,    58 
dye  compounds,  193 
microscopical     examination 

of,  231 
physical    properties    of,    1 1 , 

141,  142,  171 

reactions  of,  76,  169,  186 
state  of,  72,  in,  1 17 


312 


INDEX 


Fibroin,  27,  -195 
Pick's  law,  1 66 
Flax,  79 

Fluorescence,  170 
Formaldehyde,  action  of,  98 
Fuchsine,  33 

GALLIC  acid,  action  of,  128,  158 
absorption  by  colloids,  158, 

163 

cotton,  162 

silk,  158 

hide  powder,  164 
Gelatine,  action  of,  163,  173 
Glucosides,  231 
Gly eerie  acid,  28 
Glycocol,  29 
Greiss'  reaction,  36 
Guldberg's  law,  154 

HEMP,  79 

Homatropine  hydrochloride,  207 
Hood's  law,  99,  148 
Hydrate  theory  of  solution,  103 
Hydrated  irons,  104 
Hydration,  non-reversible,  268 
Hydrazine  grouping,  222 
Hydrocellulose,  13,  79,  82 
Hydrogels,  in,  116 
Hydrogel  state,  in,  116,  125 
Hydrolysis,  21,  129 
Hydrosol  state,  in,  116,  125 
Hydrosols,  in,  279 
Hydrosulphites,  50 
Hydroxyanthraquinones,  40 
Hydroxyazobenzenes,  213 
Hystazarine,  40 

INDIGO,  32,  295 

dyeing,   144,   185,  220,  259, 

275 

salt,  295 
Ingrain  colours,  173,  197 

resistance  to  soap,  198,  202 

on  cotton,  204,  218 

on  silk,  195,  217 
Ionic  theory,  104 


Ionic  hydrates,  104 

Ions,  1 06 

Isonitrolic  acid,  169 

Iron  mordants,  43,  60,  65,  68 

JUTE,  79,  172 

dyeing  of,  172 

KERATINE,  24,  98 
Kermes,  2 

LACTIC  acid,  28 
Lakes,  56,  61,  240 

albumen,  83,  192,  244 

alizarine,  38,  43,  56 

double,  56 

fatty  acids  in,  60 

fugitive,  241 

nature  of.  58,  43,   190,  241, 

243 

steaming,  60 
Lanuginic  acid,  25 

reactions  of,  25 
Laws  of  aggregation,  266 

chemical  action,  148,  154 

diffusion,  165 

distribution,  154 

dyeing,  146,  154,  171,  176 

levelling  up,  114 
Leucine  /3,  29 

Leuco  compounds,  37,  48,  50 
Lichens,  dye  from,  2 
Liebermann  and  v .  Kostanecki's 

law,  39 

Light,  action  of,  30,  60,  135,  281, 
282,  291 

in  vacuo,  289 

on  anthracene,  285 

on  dehydration,  296 

on  dyes,  291,  295 

onnatural  colouring-matters, 
294 

on  organic  compounds,  282, 

294 

theory  of,  288 

Liquids  degraded  to  solid  state, 
23 


INDEX 


313 


Liquids,  mutual  solubility  of ,  133 
Liquocellulose,  81 
Logwood,  32 
lakes,  256 

MADDER,  32 

Magenta,  170,  188,  193,  239,  249 

alkylation  of,  228 

base,  227 

Magnesium  chloride,  21 
Mass  action,  190,  248 

laws  of,  190 
Mauveine,  33,  100 
Mechanical  theory  of  dyeing,    7, 

142 

Mechanico-chemical  theory,   150 
Membranes,  112 

diffusion  through,  1 1 2 

inert,  112 

semi-permeable,  113 
Mercerised  cotton,  19,  133,  237 

heat  developed  during,  20 

linen,  20 

Metallic  salts,  218 
Metastannic  acid,  225 
Metatungstate  of  soda,  286 
Methyl  violet,  249 
Millon's  reagent,  25 
Mineral  colours,  4 
Moisture,      influence      of,      132, 

149 
Molecular  conductivity,  106 

migration,  113,  255 

state,  51,  252 
Mordants,  4,  53,  61 

aluminium,  53,  61,  65 

basic,  53 

chromium,  43,  63,  68 

copper,  45,  65 

fatty  acids,  56 

iron,  43,  60,  65,  68 

nickel,  66 

on  cotton,  53 
silk,  53 
wool,  53 

tin,  43,  57,  68 

titanium,  66 


Mordant  dyes,  38,  40 
Mordanting  action,  143,  157,  184, 

»     236 

i 

NAPTHIONIC  acid,  209 
Naphthol  sulphonic  acid  R.,  209 
Neutral  salts,  action  of,  96,  259 
Nickel  mordants,  66 
Night  blue,  193,  270 

lakes,  193,  205 
Nitro-amidophenolsulphonic 

acid,  41 

Nitro-cellulose,  16,  20,  185 
Nitrophenolsulphoazo  -  j3  -  naph- 

thol,  41 

Nitrosalycilic  acid,  46 
Nitroso  dyes,  41,  45 
Nitrosophenols,  40 
Nitrous  acid,  action  of,  194 

OIL  mordants,  57 

One-bath  dyeing,  114 

Optical   properties  of   solutions, 

137 

Orchil,  32 

Orthohydioxyazobenzol  -  p.-  sul- 
phonic acid,  41 

Ortho-oximes,  40 

Orthoquinonedioximes,  40 

Osmosis,  114,  164 

Osmotic  pressure,  114 

Oxycellulose,  19,  220 

Oxygen  theory,  289 

Ozone,  action  of,  289 

PARANITRANILINE  red,  201 
Paranitrodiazobenzene,  201 
Pentatomic  nitrogen,  222 
Persulphates,  50 
Phenolic  dyes,  40,  195 
Photochemical  rays,  28 1 
Phototropical  rays,  282 
Photophysical  rays,  281 
Physical  action,  8,  140 
Picric  acid,  40,  51,  52,  176,  186, 

189 

Primary  attraction,  104 
21 


INDEX 


Primuline  colours,  152,  200 
Pseudo  solution,   104,   108,   134, 

246 

of  dyes,  239 
Purple  of  Tyre,  i 
Pyrogallol,  160 

QUINIZARINE,  40 
Quinone  theory,  37 

RAMIE,  79 

Research,  methods  of,  297 

Reversible  actions,  99,  161,  171, 

248 

Rhamnosides,  232 
Ricinoleic  acid,  59 

aluminium,  salt  of,  59 
Rosaniline  hydrochloride,  48 

acetate,  99 

SALTS,  action  of,  in  dyeing,  96 
Salt  formation  theory,  228 
Sand,  action  of,  on  solutions,  145 

action  in  dyeing,  147 
Schiff's  reaction,  19 
Secondary  attraction,  104,  273 
Serene,  28 
Sericine,  28 

Silica,  effect  of  wetting,  22 
Silicic  acid,  1 16 
Silk,  27,  141,  182,  204 

acids  on,  30,  84,  179 

alkalies  on,  30,  76 

analysis  of,  27 

bleaching,  75 

boiling  off,  73 

composition  of,  27,  230 

decomposition  of,  28 

fibroin,  27 

gum,  27,  73 

mordants  on,  68 
theories  of,  70 

primuline  dyes  on,  201 

solution  of,  31 

Single  bath  dyeing,  62,  114,  256 
Soap,  action  on  silk,  75 

in  Turkey  Red  dyeing,  58 


Sodium  carbonate,  74 

sulphate,  98,  152 
Solid  solution,   8,  43,    168,    174, 

190 

Solids,  action  on  wetting,  22 
Soluble  oil,  59 
Solutions,  51,  103,  104,  f26,  249 

chemical  action  in,  125 

concentrated,  253 

non-reversible,  125 

of  colloids,    1 08,    246,    256, 

277 
Solubility,  105 

of  dyes,  132,  166 
Solvent  action,  166 
Stannic  acid,  225 
Stannic  chloride,  68 
Steaming,  60 

Stereochemical  examination,  207 
Strength  of  fibres,  17 

dye  solutions,  102 
Suint,  78 

Sulphanilic  acid,  209 
Sulphonic  acids,  35,  95,  190,  238 
Sulphur  dyes,  46,  219,  276 
Sulphuric  acid  on  wool,  88 
Sumacing,  57 
Surface  action,  183 
Surface  character  of  fibres,  266 
Surface  concentration,  246,  253, 

262,  264 

Surface  energy,  262 
Surface  tension,  266 
Surface  viscosity,  265 

TANNIC  acid,  66,  128,  240,  272 
absorption  of,  66,  158,  160, 

164,  220,  237 
lakes,  66,  237 
nature  of,  66,  237 

Tanning,  157 

Temperature  of  dyeing,  100,  102, 

147,  152,  269 
mordanting,  69,  157 
on  wetting  solids,  22 
influence  of,  69,  100,  234 

Tervalent  oxygen,  105 


INDEX 


315 


Tetranitrochrysazarine,  40 
Tetrazo  dyes,  36 
Thermochemical    reactions,    223 
Thiazine  derivatives,  47 
Tin  mordants,  59 
Trihydroxybenzenes,  160 
Trinitroresorcinol,  40 
Turkey  Red,  55 
Tyrosine,  28,  29,  204,  205 

ULTRA-MICROSCOPICAL   measure- 
ment, 157 

VARIATION  in  shade  on  dyeing, 

241 

Victoria  Blue  4R.,  145 
Viscose,  13 

WEIGHTED  silk,  277 
Woad,  3 


Wool,  24,  141 

acids  on,  24,  62,  77,  84,  87, 

154,  156 

alcoholic  potash  on,  77 
alkalies  on,  26,  77 
bleaching,  94 
composition  of,  26 
dyeing,    91,    153,    166,    170, 

182,  204,  230 
fatty  acids  in,  78 
hydrolysis  of,  77 
ingrain  colours  on,  217 
mordants  on,  26,  61 
nitrous  acid  on,  24,  30 
physical  structure  of,  24 
preliminary    treatment    of, 

94,  191 

sodium  sulphate,  on,  98 
sulphonic  acids  on,  95,  154 
sulphur  in,  24 


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